Add a mode for session_trace_match to log once per message

Currently session_trace_match only logs the output if one of the captured lines matches when the session is about to close. Sometimes it's valuable to be able to capture a snapshot of the in-memory info log when some message is logged but before the session actually stops. Some way of controlling when the matching is done is needed.

One option is to add a new parameter, session_trace_dump=[unexpected|match_stop|match_line].

• unexpected is the current unconditional dump that happenswhen unexpected conditions occur (e.g. unexpected responses from server, unexpected packet types, unknown PS IDs)
• match_stop is the current behavior when one of the captures lines matches the pattern in session_trace_match
• match_line would be a new option that dumps the current log whenever a matching line is logged. This could also optionally clear the trace log so that if the same message is logged again, only the new messages are written into the trace dump.