Add merged patches to commit title in merge-to-branch.

This makes it easier to grep for patches in title in the revision history.

This also removes the redundant information into which branch was merged, as this can be derived from the version number in the title now.

BUG=
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/223753002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20482 ce2b1a6d-e550-0410-aec6-3dcde31c8c00