add sipsimple.green.session2.GreenSession class

darcs-hash:20090305161358-b2873-683031ce0d8853d8c7db34855546eb1d1026a0b8
add sip_send_message.py as an example and test for GreenSession

darcs-hash:20090305161444-b2873-a6fda07f03f5478ac750834ed8029b4e7e03ba75