Fix application of patch files created with `git diff --no-prefix --relative .`

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1659 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Fix check_revision.py to not throw exceptions when using a Chromium git checkout.

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1661 5089003a-bbd8-11dd-ad1f-f1f9622dbc98