This change makes a few improvements to our Mercurial support:

The way that binary files were appearing in diffs was causing the

   diff parser (based on the GitDiffParser) to override the commit IDs

   in the filediff revisions with the file SHAs that hg diff --git was

   adding. The file SHAs have no meaning to us, so these have been

   replaced back with the commit IDs.
I've started seeing warnings pop up about unclosed resources when

   dealing with Popen. Treating the object as a context manager fixes

   this.

Ran unit tests.
Posted a bunch of changes, including binary files.