Add a test module for the event API, test_event.c.

Add a test module for the event API, test_event.c.

This module includes a single test so far that creates events using two
different methods and does some verification on the result to make sure
the correct data can be retrieved from the event that was created.

One bug was found in the event API while developing this test, which makes
me happy.  :-)

Review: https://reviewboard.asterisk.org/r/495/

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@246260 65c4cc65-6c06-0410-ace0-fbb531ad65f3