Small improvements to push-to-trunk.sh and merge-to-branch.sh.

Small improvements to push-to-trunk.sh and merge-to-branch.sh.

1.) When a back-merged patch applied at an offset, ignore the "Hunk #1 succeeded at ..." lines instead of printing a scary warning.
2.) When push-to-trunk was not called with "-c /path/to/chrome/src", explicitly ask for the path to help discoverability of the feature.
3.) Correctly convert "BUG=chromium:123" to "(Chromium issue 123)" in the pre-made ChangeLog entry.

Review URL: https://chromiumcodereview.appspot.com/10073010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11321 ce2b1a6d-e550-0410-aec6-3dcde31c8c00