Fix memory leak while loading modules, adding formats, and destroying endpoints

This patch fixes three memory leaks
 * When we load a module with the LOAD_PRIORITY flag, we remove its entry from
   the load order list. Unfortunately, we don't free the memory associated with
   entry in the list. This patch corrects that and properly frees the memory
   for the module in the list.

 * When adding a custom format (such as SILK or CELT), the routine for adding
   the format was leaking a reference. RAII_VAR cleans this up properly.

 * We now de-ref the channel_snapshot appropriately when an endpoint is
   disposed of
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Merged revisions 391489 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 391507 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@391521 65c4cc65-6c06-0410-ace0-fbb531ad65f3