svndiff.py: add support for git checkouts
(and yes, we should probably rename the tool soon)

R=senorblanco@chromium.org

Review URL: https://codereview.chromium.org/19512002

git-svn-id: http://skia.googlecode.com/svn/trunk@10153 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed