Added PJSIP 2.x source tree as of r4531

Ignore-this: 816386b402495899d0b914cdbbd37a7b

Some changes were made to the source tree before importing:
  - Removed tests
  - Removed pjsip-apps
  - Removed portaudio

darcs-hash:20130606135931-56b4d-f1e5ece1a81b720cba91bd7987161c1a413fe9e3
pjsip: Fixed updating local direction if SDP answer is inactive

Ignore-this: 1ce6d3c138218b8cf7f4d6cb0de4b2f2

http://lists.pjsip.org/pipermail/pjsip_lists.pjsip.org/2013-January/015584.html

darcs-hash:20130606144009-56b4d-7234a683166d4560874b9b3551e0d424b7fca612
pjsip: Don't tear down dialog if 408 is received for in-dialog requests

Ignore-this: cadc9ddb7cb63813d135e18c9ff9fa5f

darcs-hash:20130606144111-56b4d-3c78fda50f935985ae8ca7426d735e05ede6601d