Add 'git recommit' as an easy to way to re-commit after a lint failure.

Summary:
If the lint-hook fails, the git commit message is saved in
.git/commit.save.  This makes it easy to fix the lint error and then
commit again, by running
   git recommit
If you had run 'git commit -a ...' the first time, you'd do
   git recommit -a

Test Plan: I've been using this locally for forever.

Reviewers: alan

Reviewed By: alan

Differential Revision: http://phabricator.khanacademy.org/D11346