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

lib/db/postgres7.sql

@@ -127,6 +127,7 @@ CREATE TABLE prefix_log (
    ip varchar(15) NOT NULL default '',
    course integer NOT NULL default '0',
    module varchar(20) NOT NULL default '',
+   cmid integer NOT NULL default '0',
    action varchar(20) NOT NULL default '',
    url varchar(100) NOT NULL default '',
    info varchar(255) NOT NULL default ''