channel locking: Add locking for channel snapshot creation

Original commit message by mmichelson (asterisk 12 r403311):

"This adds channel locks around calls to create channel snapshots as well
as other functions which operate on a channel and then end up
creating a channel snapshot. Functions that expect the channel to be
locked prior to being called have had their documentation updated to
indicate such."

The above was initially committed and then reverted at r403398.  The problem
was found to be in core_local.c in the publish_local_bridge_message function.
The ast_unreal_lock_all function locks and adds a reference to the returned
channels and while they were being unlocked they were not being unreffed when
no longer needed.  Fixed by unreffing the channels.

Also in bridge.c a lock was obtained on "other->chan", but then an attempt was
made to unlock "other" and not the previously locked channel.  Fixed by
unlocking "other->chan"

(closes issue ASTERISK-22709)
Reported by: John Bigelow
........

Merged revisions 404237 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@404260 f38db490-d61c-443f-a65b-d21fe96a405b
chan_oss.c: channel being locked twice and unlocked once

Removed channel lock as it is now being down in ast_channel_alloc
........

Merged revisions 404261 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@404262 f38db490-d61c-443f-a65b-d21fe96a405b
ooh323c: Fix gcc 4.6.3 compiler warnings.
........

Merged revisions 404212 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 404219 from http://svn.asterisk.org/svn/asterisk/branches/11
........

Merged revisions 404263 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@404264 f38db490-d61c-443f-a65b-d21fe96a405b