[MERGE] FileCollection

[Martin Pool]

Adding such a utility could be good.

s/cand/can

FileCollection is not a very obvious name.  ListingFile?  FileListing?

It seems odd that it talks about sequence and stores them in sequence
but returns them as a set, in random order.

It seems like excessive policy to allocate the names as integers
within this file.  Why not let the caller supply them?

+    def iter_files_recursive(self):
+        Transport.iter_files_recursive(self)
+

I'd like a comment in those two methods explaining that the default
implementation raises an exception.

+    * New transport decorator 'unlistable+' which disables the list_dir
+      functionality for testing.
+

Take credit :)

-- 
Martin