A Trigger Servlet for Hudson

Have written a little Trigger Servlet for Hudson, to enable post commit builds on Google Code projects.

By relying upon a shared secret, it enables pre-authentication of the trigger url; which should only be visible to someone with administrator access to the Hudson job and
administrator access to the triggering site, for example the Google Code Administer Source page.

Managed to hit 100% line and branch coverage Yay!.