NT mode improvements:

NT mode improvements:

  Add channel hunting in case the TE side specifies "any" channel in the Channel ID IE
  of an incoming SETUP message (or if there is no Channel ID IE at all).

  Support overlap dial in NT mode, (needed for BRI phones), triggered by a missing
  Called Party IE in the SETUP message.

  Tones... picking up a phone and not hearing a dialtone is no fun...
  Dialtone (works) and Ring (untested) are implemented, tones are generated by
  a secondary thread (only started for spans in NT mode). I tried to do the tone
  generating in the main thread first, but it is easier to handle like this.
  The loop uses the first channel that needs tones as a timing reference and the
  tone buffer is reused if multiple succeeding channels share the same state to
  save some cpu cycles (yes, not perfect... alternative is to allocate a buffer for
  every indication and precalculate the values... => 16KB for each indication).

  Coming up next: Q.931 Timers

git-svn-id: http://svn.openzap.org/svn/openzap/trunk@544 a93c3328-9c30-0410-af19-c9cd2b2d52af