Fix svn tags in release scripts.

Rebase the local branch after committing so that git svn
tag works.

Some of these changes need to be ported to git in https://codereview.chromium.org/607893004/

BUG=chromium:410721,v8:3601
LOG=n
TEST=script_test.py
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/618703002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24330 ce2b1a6d-e550-0410-aec6-3dcde31c8c00