datalib:add_to_log() - avoid schema lookups, pace updates to user and user_lastaccess
datalib:add_to_log() - avoid schema lookups, pace updates to user and user_lastaccess

* All updates to user.lastaccess and user_lastaccess.timeaccess are paced to
60s of the last update on the same record -- this should reduce the heat
on those tables.

* Updates/inserts to user_lastaccess are down with raw SQL to avoid costly
schema lookups on every request.

dilawar/moodle