PickupChan: Add ability to specify channel uniqueids as well as channel names.

* Made PickupChan() search by channel uniqueids if the search could not
find a channel by name.

* Ensured PickupChan() never considers the picking channel for pickup.

* Made PickupChan() option p use a common search by name routine.  The
original search was erroneously case sensitive.

(issue AFS-42)

Review: https://reviewboard.asterisk.org/r/3017/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403013 65c4cc65-6c06-0410-ace0-fbb531ad65f3