Add ast_event subscription unit test and fix some ast_event API bugs.

This patch introduces another test in test_event.c that exercises most of the
subscription related ast_event API calls.  I made some minor additions to the
existing event allocation test to increase API coverage by the test code.
Finally, I made a list in a comment of API calls not yet touched by the test
module as a to-do list for future test development.

During the development of this test code, I discovered a number of bugs in
the event API.

1) subscriptions to AST_EVENT_ALL were not handled appropriately in a couple
   of different places.  The API allows a subscription to all event types,
   but with IE parameters, just as if it was a subscription to a specific
   event type.  However, the parameters were being ignored.  This affected
   ast_event_check_subscriber() and event distribution to subscribers.

2) Some of the logic in ast_event_check_subscriber() for checking subscriptions
   against query parameters was wrong.

Review: https://reviewboard.asterisk.org/r/617/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@258632 65c4cc65-6c06-0410-ace0-fbb531ad65f3