LP#1200735: improve performance of patron search by username

This patch adds an additional index on actor.usr.usrname.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Bill Erickson <berick@esilibrary.com>
LP1200735 stamping upgrade for usrname index

Signed-off-by: Bill Erickson <berick@esilibrary.com>