wireproto: advertise supported media types and compression formats This commit introduces support for advertising a server's support for media types and compression formats in accordance with the spec defined in internals.wireproto. The bulk of the new code is a helper function in wireproto.py to obtain a prioritized list of compression engines available to the wire protocol. While not utilized yet, we implement support for obtaining the list of compression engines advertised by the client. The upcoming HTTP protocol enhancements are a bit lower-level than existing tests (most existing tests are command centric). So, this commit establishes a new test file that will be appropriate for holding tests around the functionality of the HTTP protocol itself. Rounding out this change, `hg debuginstall` now prints compression engines available to the server.