Log Message:
Update thin to 1.5.1.

== 1.5.1 Straight Razor
 * Fix issue when running as another user/group without a PID file.
 * Allow overriding Connection & Server response headers.
 * Update vlad example [Mathieu Lemoine]
 * Keep connections in a Hash to speedup deletion [slivu]
 * Force kill using already known pid. Prevents "thin stop" from leaving
   a process that removed its pid file, but is still running (e.g. hung
   on some at_exit callback) [Michal Kwiatkowski]