The current behavior of 'pjsip send unregister' is to send the unregister
(REGISTER with 0 exp) but let the next scheduled register proceed normally.
I don't think that's a good idea.  If you unregister, it should stay
unregistered until you decide to start registrations again.  So this patch
just adds a cancel_registration call to the current unregister_task to
cancel the timer.

Of course, now you need  a way to start registration again so I've added
a 'pjsip send register' command that unregisters and cancels any existing
registration (the same as send unregister), then sends an immediate
registration and starts the timer back up again.

Both changes also ripple to AMI.  There's a new PJSIPRegister command.

There's no harm in calling either command repeatedly.  They don't care
about the actual state.

Tested-by: George Joseph

Review: https://reviewboard.asterisk.org/r/4301/
........

Merged revisions 430223 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430224 65c4cc65-6c06-0410-ace0-fbb531ad65f3