+ i.e. this is the same as the above except that its apply() method
+ will return true not only if the contents to be written are
+ identical to the contents of filename on the disk but also it
+ returns true if there exists some other file sitting in the same
+ directory which already contains those identical contents.
+
+ >>> testfile = '/tmp/directory_filter_text_f39e5b58-c260-40da-9448-ad1c3b2a69c3.txt'
+
+ >>> contents = b'This is a test'
+ >>> with open(testfile, 'wb') as wf:
+ ... wf.write(contents)
+ 14
+
+ >>> d = DirectoryAllFilesFilter('/tmp')
+
+ >>> d.apply(contents) # False is _any_ file in /tmp contains contents
+ False
+
+ >>> d.apply(b'That was a test') # True otherwise
+ True
+
+ >>> os.remove(testfile)
+ """