sip_im_session fix: history_file attribute was not properly initialized for incoming sessions

darcs-hash:20090129080914-b2873-05a9f97c8dbe8aab95925a38ecb692007109ccf4
sip_im_session: create directory for history if it does not exist

darcs-hash:20090129080950-b2873-0876fe2097bddecf6062e26e877fe52e4bb46fd2