Bug 18821: TrackLastPatronActivity is a performance killer

Bug 18821: TrackLastPatronActivity is a performance killer

Test Plan:
1) Apply this patch
2) Start a new session ( a private browser window works well )
3) Note the lastseen column in the borrowers table is updated
4) Browse a few pages, not the lastseen column is not updated again
5) Close the browser window and repeat steps 2-4
6) prove t/db_dependent/Auth.t

Signed-off-by: Charles Farmer <charles.farmer@inLibro.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>