Specify wa_group result set column name using escaped double-quotes

When specifying the name of the result set column for wa_group, use
escaped double-quotes instead of back-tick notation.  With this
change, the Stanford WebAuth Module now works when the Drupal database
back-end is PostgreSQL.

Tested Data Base Environments:

 - PostgreSQL 9.1.6
 - MySQL 5.1.67