We had an online-only unit test for Mercurial that attempted to query

something from the pypy repository on Bitbucket. This doesn't exist now,

since Bitbucket doesn't support Mercurial anymore, preventing the test

from passing.
This change fixes the test to access content from the main Mercurial

repository instead. The test is also altered slightly to ensure that

the revision is properly considered alongside the filename.

Unit tests pass.