Fix memory leak in error paths for action_originate().

Fix memory leak in error paths for action_originate().

* Fix memory leak of vars in error paths for action_originate().

* Moved struct fast_originate_helper tech and data members to stringfields.

* Simplified ActionID header handling for fast_originate().

* Added doxygen note to ast_request() and ast_call() and the associated
channel callbacks that the data/addr parameters should be treated as const
char *.

Review: https://reviewboard.asterisk.org/r/1690/
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Merged revisions 353454 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 353463 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@353466 65c4cc65-6c06-0410-ace0-fbb531ad65f3