Merge r613252 from trunk:

* server/mpm/prefork/prefork.c (child_main): Unlock the mutex before
  terminating in the multi-listener poll error path.

Submitted by: jorton
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@662013 13f79535-47bb-0310-9956-ffa450edef68