Add ability to handle PageReference return from Site.login class
https://gus.my.salesforce.com/apex/adm_userstorydetail?id=a07B0000000eOHH&sfdc.override=1
@rev dchasman@
@P4Cl:8895503@
@bug W-2177192@
Merging origin/aballard/master-pending-redirect into master