[gitolite] denying access by factors other than ref/path names

Gitolite now allows you to deny access using data other than ref names or path names.

For example, you can deny a push if:

  * it adds more then N new files (or variations, like changed
    files, binary files, new binary files...)
  * it contains autogenerated files that can't be caught by
    gitignore
  * it fails a "no non-merge first-parents" rule
  * you don't like the phase of the moon :)

Since the actual decision is done by a script you write, you can enforce pretty much any site-specific stupi^Wstandards, (like ensuring that junior developers push only their own commits).

http://sitaramc.github.com/gitolite/vref.html has all the gory details for anyone interested, and contrib/VREF in the latest pu branch has example code.