added pypjua.clients.sdputil: parsing file-selector of SDP

darcs-hash:20081128125546-b2873-e58489c23a32085817791078b00cd9e2d11a4c7a
sip_im_session.py: accept sessions with file transfers

darcs-hash:20081128125613-b2873-8b94ed1dc2ddb50e5c5f8bea49599999d2e0662d