[PATCH 0 of 3 V7] hgweb: teach archive how to handle file patterns

[Angel Ezquerra]

This version addresses the issues raised by Pierre-Yves David. In particular:
- I added a new test (we now test downloading a single file, a single directory and that we reject patterns).
- We explicitly check that no known pattern has been used, raising a 403 HTTP error if one is used. If a (future) unknown pattern were ever used we would simply return an empty archive.

I also fixed a couple of typos and improved the commit message of the second patch in the series a bit.

Is sending 7 versions of the same series a record? :-)