We ran into a problem where the diff is generated properly and git doesn't throw an error, but it prints warnings to stderr during the diff generation. The error stream content is included in the diff and this creates a corrupted diff, which causes breakage on the Review Board server. This patch makes it so that the generated diffs don't include the stderr stream content.
Sample Warning:

   warning: CRLF will be replaced by LF in pom.xml.

   The file will have its original line endings in your working directory.

We tested that the scenario described no longer occurs when the stderr is not included in the diff.