Pre-commit checks

[Owen Taylor <otaylor redhat com>]

I've written a set of pre-commit checks that more or replace the current
SVN checks.

Three scripts:

http://git.gnome.org/cgit/gitadmin-bin/tree/pre-receive-check-policy

  Forbids many sorts of foot-shooting. I went pretty aggressive here
  and blocked, along with less controversial things:
 
   Creating lightweight tags except on initial import
   Deleting tags (may have to drop this one at least temporarily for
    tag cleanup from the svn import)
   Replacing tags

  You'll note that some of the messages reference pages on
  git.gnome.org. Assistance in writing those pages much appreciated!
  (as are improvements to the messages.)

http://git.gnome.org/cgit/gitadmin-bin/tree/pre-receive-check-maintainers

  Requires a MAINTAINERS file on the master branch. 

http://git.gnome.org/cgit/gitadmin-bin/tree/pre-receive-check-po

  Checks that .po files pass msgfmt and are not executable.

I haven't yet gone through and installed these hooks in our existing
repositories (there's a gnome-pre-receive that can be symlinked into
place to run all of them), but I think things are in pretty good
shape in this area.

- Owen