Two new Git policy checks

[Owen Taylor <otaylor redhat com>]

I added two checks that get on each "new" commit that wasn't previously
in the repository. (Excluding the import phase.) Like all the other
Git/Help pages the referenced pages haven't been written yet.

Check 1: User hasn't configured their email address
===================================================

If a commit has an Author: email that ends in 'localhost.localdomain'
or '(none)', then the push errors out with:

---
The commits you are trying to push contain the author email
address '$email'. Please configure your
username and email address. See:

  http://live.gnome.org/Git/Help/AuthorEmail

For instructions about how to do this and how to fix your
existing commits.
---

Check 2: git pull introduced stray merges
=========================================

If a commit has a subject that matches

 Merge branch.*of.*\(git\|ssh\):

Then the commit errors out with:

---
The commit:

[git log output for commit]

Looks like it was produced by typing 'git pull' without the --rebase
option when you had local changes. Running 'git  pull --rebase' now
will fix the problem. Then please try, 'git push' again. Please see:

  http://live.gnome.org/Git/Help/ExtraMergeCommits
---

If you look through the commit lists, we are getting a lot of these
stray merges, even from people that should know better :-)