Add example for cleaning when top==out.

playground/top_eq_out/.gitignore

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+.lock-w*
+.conf_check_*
+config.log
+c4che

playground/top_eq_out/a.cpp

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+int truc=5;
+

playground/top_eq_out/wscript

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+#! /usr/bin/env python
+# encoding: utf-8
+
+"""
+Example providing a clean context for when top==out.
+
+When top==out, waf will not do anything by default
+in the clean context, because it could be dangerous.
+You need to do something for your particular use case.
+This example will remove all the generated files that
+will appear under out.
+
+The distclean operation, which normally removes the build folder
+completely plus some files, is also modified to remove
+the rest of waf-generated files.
+
+Notes:
+
+- this example won't work when using dynamic builds.
+  
+  This is because it uses the tasks output files, which 
+  are known in advance.
+
+  For it to work, you would need to store the outputs of
+  dynamic builds somewhere.
+
+  But top == out is a rare case, so why bother.
+
+
+
+"""
+
+VERSION='0.0.1'
+APPNAME='clean_test'
+
+top = '.'
+out = '.'
+
+def options(opt):
+	opt.load('compiler_cxx')
+
+def configure(conf):
+	conf.load('compiler_cxx')
+	conf.check(header_name='stdio.h', features='cxx cxxprogram', mandatory=False)
+
+def build(bld):
+	bld(features='cxx', source='a.cpp', target='pouet')
+
+	if bld.cmd == 'clean':
+		for tgen in bld.get_all_task_gen():
+			tgen.post()
+			for t in tgen.tasks:
+				for n in t.outputs:
+					if n.is_child_of(bld.bldnode):
+						n.delete()
+
+
+def distclean(ctx):
+	import os, shutil
+	from waflib import Context
+
+	for fn in os.listdir('.'):
+		if fn.startswith('.conf_check_') or fn.startswith(".lock-w") \
+		 or fn in (Context.DBFILE, 'config.log') \
+		 or fn == 'c4che':
+			if os.path.isdir(fn):
+				shutil.rmtree(fn)
+			else:
+				os.unlink(fn)
+
+