title: Writing a git post-receive hook to deal with a specific branch
body: <p>Here's my current hook in a bare repo that lives in the company's server:
  <code>git push origin master</code>
  This hooks pushes to Assembla.
  What i need is to push only one branch (master, ideally) when someone pushes changes to that  branch on our server, and ignore pushes to other branches. Is it possible to select the branch  from a bare repo and push only that branch to Assembla?</p>