Adding a new dialplan function AUDIOHOOK_INHERIT

This function is being added as a method to allow for
an audiohook to move to a new channel during a channel
masquerade. The most obvious use for such a facility is
for MixMonitor when a transfer is performed. Prior to
the addition of this functionality, if a channel 
running MixMonitor was transferred by another party, then
the recording would stop once the transfer had completed.
By using AUDIOHOOK_INHERIT, you can make MixMonitor 
continue recording the call even after the transfer
has completed.

It has also been determined that since this is seen
by most as a bug fix and is not an invasive change,
this functionality will also be backported to 1.4 and
merged into the 1.6.0 branches, even though they are
feature-frozen.

(closes issue #13538)
Reported by: mbit
Patches:
      13538.patch uploaded by putnopvut (license 60)
	  Tested by: putnopvut

Review: http://reviewboard.digium.com/r/102/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@166092 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/audiohook.h

@@ -150,6 +150,21 @@ int ast_audiohook_detach(struct ast_audiohook *audiohook);
  */
 int ast_audiohook_detach_list(struct ast_audiohook_list *audiohook_list);
 
+/*! \brief Move an audiohook from one channel to a new one
+ *
+ * \todo Currently only the first audiohook of a specific source found will be moved.
+ * We should add the capability to move multiple audiohooks from a single source as well.
+ *
+ * \note It is required that both old_chan and new_chan are locked prior to calling
+ * this function. Besides needing to protect the data within the channels, not locking
+ * these channels can lead to a potential deadlock
+ *
+ * \param old_chan The source of the audiohook to move
+ * \param new_chan The destination to which we want the audiohook to move
+ * \param source The source of the audiohook we want to move
+ */
+void ast_audiohook_move_by_source(struct ast_channel *old_chan, struct ast_channel *new_chan, const char *source);
+
 /*! 
  * \brief Detach specified source audiohook from channel
  *