Changed default value of file_transfer.directory to None

Ignore-this: 2b1489922e7a1177c31329d994bc8d36

darcs-hash:20091113102641-1e3d8-e40ec80d3bc85e2f3eb64d62c871ce0466d43a3c
Fixed posting of SIPSessionGotProvisionalResponse notifications

Ignore-this: 62b3a99d480f1826740d377194eea832

darcs-hash:20091113103344-1e3d8-d91735eac55d4011a0ddf2f592d9d5e3cb967c38