Release the allocated channel decreasing the reference counter.

When allocating the channel use ao2_ref(-1) to release it, instead of calling
ast_free().
Also avoid freeing structures inside that channel (on error) if they will be
released by the channel destructor being called if the reference counter reachs
0.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@200108 65c4cc65-6c06-0410-ace0-fbb531ad65f3