Support renamed files from GitHub in post-commit UI

Review Request #8577 — Created Dec. 16, 2016 and submitted — Latest diff uploaded

Information

Review Board
release-2.0.x
66a109f...

Reviewers

The GitHub client did not support generating the diff for a file renamed
in a change that was retrieved via the post-commit review UI. This has
been corrected. Additionally, the code was somewhat cleaned up to not
shadow the file global. The unit test for get_change has been
updated to add a case for renamed files.

Used the post-commit UI to create a new review request that contained a
renamed file. It worked as expected.