Tracking branch via git hooks

References 
http://help.github.com/post-receive-hooks/
http://blog.badsyntax.co/post/3014159260/github-web-hook-post-receive

This script will respond to the JSON that github sends after a commit in a repo.
Then it will look at the branch that a commit was made and if it is a specified
branch the script will then perform a sudo to do a request pull as a specified
user for a specified local git repo.

Then the git pusher and specified admin will receive an email with the output
of the git pull and some details from the commit.

Installation

1) To use script, put it in a web accessible directory.
2) Copy/rename config.php.dist to config.php
3) Set appropiate values for config.php
4) Setup your github repo to point to this script as your post-receive hook 
   server as mentioned here: http://help.github.com/post-receive-hooks/
5) Setup apache user to run gitpull.php script has specified user. Edit sudoer 
   file with:
   apache ALL = (<USER>) NOPASSWD: <PATH_TO_SCRIPT>/gitpull.php
6) Make sure that your sudoers file has "Default requiretty" commented out, so
   that the apache user can sudo and run a string as a different user:
   http://www.zimbra.com/forums/installation/10553-solved-sudo-sorry-you-must-have-tty-run-sudo.html