Prevent git from using any external diff program that may have been configured for it when figuring out the patch to upload to the try server.  This prevents git installations where the diff is configured to use an interactive tool to work without doing nasty workarounds.
Prevent git from using any external diff program that may have been
configured for it when figuring out the patch to upload to the try
server.  This prevents git installations where the diff is configured
to use an interactive tool to work without doing nasty workarounds.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/1958002

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@47661 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools