diff --git a/playground/maxjobs2/compute/wscript b/playground/maxjobs2/compute/wscript
index b95da2a3..c160ad90 100644
--- a/playground/maxjobs2/compute/wscript
+++ b/playground/maxjobs2/compute/wscript
@@ -35,7 +35,7 @@ def lock_maxjob(self):
 		try:
 			self.lockfd = os.open(self.generator.bld.lockfile, os.O_TRUNC | os.O_CREAT | os.O_RDWR)
 			fcntl.flock(self.lockfd, fcntl.LOCK_EX | fcntl.LOCK_NB)
-		except (OSError, IOError), e:
+		except EnvironmentError as e:
 			if e.errno in (errno.EACCES, errno.EAGAIN):
 				time.sleep(0.3)
 				continue
diff --git a/waflib/Build.py b/waflib/Build.py
index 7218807e..abc6c4d1 100644
--- a/waflib/Build.py
+++ b/waflib/Build.py
@@ -410,8 +410,8 @@ class BuildContext(Context.Context):
 		:param value: value to depend on
 		:type value: :py:class:`waflib.Node.Node`, string, or function returning a string
 		"""
-		if path is None:
-			raise ValueError('Invalid input')
+		if not path:
+			raise ValueError('Invalid input path %r' % path)
 
 		if isinstance(path, waflib.Node.Node):
 			node = path
@@ -419,6 +419,8 @@ class BuildContext(Context.Context):
 			node = self.root.find_resource(path)
 		else:
 			node = self.path.find_resource(path)
+		if not node:
+			raise ValueError('Could not find the path %r' % path)
 
 		if isinstance(value, list):
 			self.deps_man[node].extend(value)
@@ -441,6 +443,8 @@ class BuildContext(Context.Context):
 			def build(bld):
 				bld.hash_env_vars(bld.env, ['CXX', 'CC'])
 
+		This method uses an internal cache.
+
 		:param env: Configuration Set
 		:type env: :py:class:`waflib.ConfigSet.ConfigSet`
 		:param vars_lst: list of variables
@@ -464,11 +468,8 @@ class BuildContext(Context.Context):
 				pass
 
 		lst = [env[a] for a in vars_lst]
-		ret = Utils.h_list(lst)
+		cache[idx] = ret = Utils.h_list(lst)
 		Logs.debug('envhash: %s %r', Utils.to_hex(ret), lst)
-
-		cache[idx] = ret
-
 		return ret
 
 	def get_tgen_by_name(self, name):
@@ -509,7 +510,7 @@ class BuildContext(Context.Context):
 
 		pc = (100.*state)/total
 		eta = str(self.timer)
-		fs = "[%%%dd/%%%dd][%%s%%2d%%%%%%s][%s][" % (n, n, ind)
+		fs = "[%%%dd/%%d][%%s%%2d%%%%%%s][%s][" % (n, ind)
 		left = fs % (state, total, col1, pc, col2)
 		right = '][%s%s%s]' % (col1, eta, col2)
 
@@ -592,7 +593,14 @@ class BuildContext(Context.Context):
 		self.get_group(group).append(tgen)
 
 	def get_group_name(self, g):
-		"""name for the group g (utility)"""
+		"""
+		Return the name of the input build group
+
+		:param g: build group object or build group index
+		:type g: integer or list
+		:return: name
+		:rtype: string
+		"""
 		if not isinstance(g, list):
 			g = self.groups[g]
 		for x in self.group_names:
@@ -620,15 +628,14 @@ class BuildContext(Context.Context):
 
 	def add_group(self, name=None, move=True):
 		"""
-		Add a new group of tasks/task generators. By default the new group becomes the default group for new task generators.
+		Add a new group of tasks/task generators. By default the new group becomes
+		the default group for new task generators. Make sure to create build groups in order.
 
 		:param name: name for this group
 		:type name: string
 		:param move: set the group created as default group (True by default)
 		:type move: bool
 		"""
-		#if self.groups and not self.groups[0].tasks:
-		#	error('add_group: an empty group is already present')
 		if name and name in self.group_names:
 			Logs.error('add_group: name %s already present', name)
 		g = []
@@ -750,7 +757,7 @@ class BuildContext(Context.Context):
 		for tg in self.groups[idx]:
 			try:
 				tasks.extend(tg.tasks)
-			except AttributeError: # not a task generator, can be the case for installation tasks
+			except AttributeError: # not a task generator
 				tasks.append(tg)
 		return tasks
 
diff --git a/waflib/Configure.py b/waflib/Configure.py
index 45ef9b70..0ea739c0 100644
--- a/waflib/Configure.py
+++ b/waflib/Configure.py
@@ -368,11 +368,11 @@ def cmd_to_list(self, cmd):
 	return cmd
 
 @conf
-def check_waf_version(self, mini='1.7.99', maxi='1.9.0', **kw):
+def check_waf_version(self, mini='1.8.99', maxi='2.0.0', **kw):
 	"""
 	Raise a Configuration error if the Waf version does not strictly match the given bounds::
 
-		conf.check_waf_version(mini='1.8.0', maxi='1.9.0')
+		conf.check_waf_version(mini='1.8.99', maxi='2.0.0')
 
 	:type  mini: number, tuple or string
 	:param mini: Minimum required version
@@ -552,9 +552,7 @@ def run_build(self, *k, **kw):
 	if cachemode == 1:
 		try:
 			proj = ConfigSet.ConfigSet(os.path.join(dir, 'cache_run_build'))
-		except OSError:
-			pass
-		except IOError:
+		except EnvironmentError:
 			pass
 		else:
 			ret = proj['cache_run_build']
@@ -576,11 +574,9 @@ def run_build(self, *k, **kw):
 	bld.all_envs.update(self.all_envs) # not really necessary
 	bld.env = kw['env']
 
-	# OMG huge hack
 	bld.kw = kw
 	bld.conf = self
 	kw['build_fun'](bld)
-
 	ret = -1
 	try:
 		try:
@@ -598,7 +594,6 @@ def run_build(self, *k, **kw):
 			proj.store(os.path.join(dir, 'cache_run_build'))
 		else:
 			shutil.rmtree(dir)
-
 	return ret
 
 @conf
diff --git a/waflib/Context.py b/waflib/Context.py
index ec710b90..a89db1be 100644
--- a/waflib/Context.py
+++ b/waflib/Context.py
@@ -96,7 +96,7 @@ class store_context(type):
 		super(store_context, cls).__init__(name, bases, dict)
 		name = cls.__name__
 
-		if name == 'ctx' or name == 'Context':
+		if name in ('ctx', 'Context'):
 			return
 
 		try:
diff --git a/waflib/Scripting.py b/waflib/Scripting.py
index 75d9af4a..63caec5c 100644
--- a/waflib/Scripting.py
+++ b/waflib/Scripting.py
@@ -312,9 +312,7 @@ def distclean(ctx):
 			if proj['out_dir'] != proj['top_dir']:
 				try:
 					shutil.rmtree(proj['out_dir'])
-				except IOError:
-					pass
-				except OSError as e:
+				except EnvironmentError as e:
 					if e.errno != errno.ENOENT:
 						Logs.warn('Could not remove %r', proj['out_dir'])
 			else:
diff --git a/waflib/Task.py b/waflib/Task.py
index c9bf6882..810a5b46 100644
--- a/waflib/Task.py
+++ b/waflib/Task.py
@@ -720,7 +720,7 @@ class Task(TaskBase):
 		# recompute the signature and return it
 		try:
 			bld.imp_sigs[key] = self.compute_sig_implicit_deps()
-		except (OSError, IOError):
+		except EnvironmentError:
 			for k in bld.node_deps.get(self.uid(), []):
 				if not k.exists():
 					Logs.warn('Dependency %r for %r is missing: check the task declaration and the build order!', k, self)
diff --git a/waflib/Tools/ccroot.py b/waflib/Tools/ccroot.py
index 052a81ae..700873f0 100644
--- a/waflib/Tools/ccroot.py
+++ b/waflib/Tools/ccroot.py
@@ -663,7 +663,7 @@ def process_lib(self):
 			if node:
 				try:
 					Utils.h_file(node.abspath())
-				except (IOError, OSError):
+				except EnvironmentError:
 					raise ValueError('Could not read %r' % y)
 				break
 		else:
diff --git a/waflib/Utils.py b/waflib/Utils.py
index 62379d85..4612248a 100644
--- a/waflib/Utils.py
+++ b/waflib/Utils.py
@@ -562,7 +562,7 @@ def h_fun(fun):
 	except AttributeError:
 		try:
 			h = inspect.getsource(fun)
-		except IOError:
+		except EnvironmentError:
 			h = "nocode"
 		try:
 			fun.code = h