Fix condition where no author would be retrieved (revert on a branch for  something that was on trunk, svn info only knows about it when it's ref by trunk url).
Fix condition where no author would be retrieved (revert on a branch for 
something that was on trunk, svn info only knows about it when it's ref by trunk
url).

Also added an author override, useful for webkit merges or double reverts

Review URL: http://codereview.chromium.org/551137

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@37024 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

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