Allows ParkedCall application to specify a parkinglot.

When invoking the app parkedcall, the argument can now include '@parkinglot' after the
extension.

(closes issue #18777)
Reported by: cartama
Patches:
      0018777.diff uploaded by cartama (license 1157)

Review: https://reviewboard.asterisk.org/r/1209/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@318141 65c4cc65-6c06-0410-ace0-fbb531ad65f3