Add initial Basic Rate Interface (BRI) support...

Add initial Basic Rate Interface (BRI) support...

Short summary of changes:
    (Massive) rework of the Q.921 layer
    Q.931 changes to get BRI PTMP working and cleanups (more to come...)
    Add Hi-Layer compat and Progress IE to outgoing SETUP messages
    Improve handling of call tear-down in zap_isdn.c
    Open ZAP I/O channels after processing the dialplan for incoming calls
    Bearer Capability and Channel ID IE handling improved for BRI/PRI and A-law/u-law

    ...and a lot of other small changes

git-svn-id: http://svn.openzap.org/svn/openzap/trunk@512 a93c3328-9c30-0410-af19-c9cd2b2d52af