Add an option to skip searching the regular sys.path when loading waf tools.

Granting this control allows the avoidance of issues such as accidentally
loading the "cython" module from from Cython itself, rather than the
"cython" waf tool.
Conflicts:
	waflib/Configure.py
	waflib/Context.py

waflib/Configure.py

@@ -234,7 +234,7 @@ class ConfigurationContext(Context.Context):
 			tmpenv = self.all_envs[key]
 			tmpenv.store(os.path.join(self.cachedir.abspath(), key + Build.CACHE_SUFFIX))
 
-	def load(self, input, tooldir=None, funs=None):
+	def load(self, input, tooldir=None, funs=None, loadFromSysPath=True):
 		"""
 		Load Waf tools, which will be imported whenever a build is started.
 
@@ -260,7 +260,7 @@ class ConfigurationContext(Context.Context):
 
 			module = None
 			try:
-				module = Context.load_tool(tool, tooldir, ctx=self)
+				module = Context.load_tool(tool, tooldir, ctx=self, loadFromSysPath=loadFromSysPath)
 			except ImportError as e:
 				self.fatal('Could not load the Waf tool %r from %r\n%s' % (tool, sys.path, e))
 			except Exception as e:

waflib/Context.py

@@ -210,9 +210,10 @@ class Context(ctx):
 		"""
 		tools = Utils.to_list(tool_list)
 		path = Utils.to_list(kw.get('tooldir', ''))
+		loadFromSysPath = kw.get('loadFromSysPath', True)
 
 		for t in tools:
-			module = load_tool(t, path)
+			module = load_tool(t, path, loadFromSysPath=loadFromSysPath)
 			fun = getattr(module, kw.get('name', self.fun), None)
 			if fun:
 				fun(self)
@@ -627,7 +628,7 @@ def load_module(path, encoding=None):
 
 	return module
 
-def load_tool(tool, tooldir=None, ctx=None):
+def load_tool(tool, tooldir=None, ctx=None, loadFromSysPath=True):
 	"""
 	Import a Waf tool (python module), and store it in the dict :py:const:`waflib.Context.Context.tools`
 
@@ -635,33 +636,44 @@ def load_tool(tool, tooldir=None, ctx=None):
 	:param tool: Name of the tool
 	:type  tooldir: list
 	:param tooldir: List of directories to search for the tool module
+	:type  loadFromSysPath: boolean
+	:param loadFromSysPath: whether or not to search the regular sys.path, besides waf_dir and potentially given tooldirs
 	"""
 	if tool == 'java':
 		tool = 'javaw' # jython
 	else:
 		tool = tool.replace('++', 'xx')
 
-	if tooldir:
-		assert isinstance(tooldir, list)
-		sys.path = tooldir + sys.path
-		try:
-			__import__(tool)
+	origSysPath = sys.path
+	if not loadFromSysPath: sys.path = []
+	try:
+		if tooldir:
+			assert isinstance(tooldir, list)
+			sys.path = tooldir + sys.path
+			try:
+				__import__(tool)
+			finally:
+				for d in tooldir:
+					sys.path.remove(d)
 			ret = sys.modules[tool]
 			Context.tools[tool] = ret
 			return ret
-		finally:
-			for d in tooldir:
-				sys.path.remove(d)
-	else:
-		for x in ('waflib.Tools.%s', 'waflib.extras.%s', 'waflib.%s', '%s'):
+		else:
+			if not loadFromSysPath: sys.path.insert(0, waf_dir)
 			try:
-				__import__(x % tool)
-				break
-			except ImportError:
-				x = None
-		if x is None: # raise an exception
-			__import__(tool)
-		ret = sys.modules[x % tool]
-		Context.tools[tool] = ret
-		return ret
+				for x in ('waflib.Tools.%s', 'waflib.extras.%s', 'waflib.%s', '%s'):
+					try:
+						__import__(x % tool)
+						break
+					except ImportError:
+						x = None
+				if x is None: # raise an exception
+					__import__(tool)
+			finally:
+				if not loadFromSysPath: sys.path.remove(waf_dir)
+			ret = sys.modules[x % tool]
+			Context.tools[tool] = ret
+			return ret
+	finally:
+		if not loadFromSysPath: sys.path += origSysPath