sip_im_session: print date in addition to time for older messages

darcs-hash:20090220153504-b2873-8076b78b9ab45b32b428377a2b5a7d9f69a2b13c
do not print traceback for PJSIP_EINVALIDURI error

darcs-hash:20090224082622-b2873-081b1bc4d2c95123c02601df8f58175f9eded814