Fix diff download for patches with Windows line endings

Review Request #10090 — Created July 16, 2018 and discarded — Latest diff uploaded

Information

Review Board
release-3.0.x

Reviewers

Review Board normalizes line endings to LF. This is a problem on Windows
where files have CRLF line endings. A downloaded raw diff file should
have the same line endings as the uploaded diff.

Bugs closed: 2916

Sucessfully ran unit tests.