OK, some big improvements to the logs.

OK, some big improvements to the logs.

Logs now include a field called modid which contains the coursemodule id.

This makes it now possible to

   - see complete logs per-activity

   - do backup/restore of logs

The upgrade process will currently try to scan all the old logs and
rebuild this field based on available data (especially forums).

STILL TO DO:  alter all the non-forum modules to send the coursemodule id