sip_im_session2.py: print more calming messages

- add a contextmanager to abstract it out

darcs-hash:20090318074119-b2873-3e0be75ab2065b6b9ac5cc59afb1112bf41b161f
sip_im_session2.py: print session state in the prompt

- add 'remote_party' attribute to ChatSession
- make calls in the background like the old script

darcs-hash:20090318074259-b2873-cd722f5703a769e9551d7e5b36b7cfc4fca84fa7