Show diffs of removed and propchanged files in Mercurial correctly

Summary:
By default, `hg log -- x` does not show commits which remove the file `x`, nor commits which only change properties on `x`. By passing the flag `--removed`, commits which remove or just change properties are shown. We expect these commits to be shown in callers (this is the default behavior in Git).

Fixes T2608.

Test Plan: Created commits which remove a file and change properties on a file. Verified `hg log --removed -- x` reported them correctly, and Diffusion showed them correctly.

Reviewers: btrahan, DurhamGoode

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2608

Differential Revision: https://secure.phabricator.com/D5656