Add a test that ensures that taskprocessor listener callbacks

are properly called.

The new test is a bit raw in that it uses magic numbers, but that
can be improved upon easily.



git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@376124 65c4cc65-6c06-0410-ace0-fbb531ad65f3