Added file transfer support to sip_session script

Ignore-this: 1f0b9086df6aa25fe9a870d803661e1c

darcs-hash:20091029121107-1e3d8-18dfa94f186b04990a52c49a4fbb729b61b52005
Changed tests to use 487 code rather than reason

Ignore-this: aed31a33d912dd40eec0e0b7fb3d7ee1

darcs-hash:20091029121213-1e3d8-266c8139db4c9f0db46808e846c2cb81616ad7e1