Merge pull request #380 from mikeh/master

MOBILE-2899
Sites list: Prevent a "stuck" HUD spinner when we have no session.
MOBILE-2900: Fix crash in - [SyncOperation main], line 97
MOBILE-2901: Fix crash in [AccountManager updateAccountStatusForAccount:completionBlock:] (AccountManager.m:303)
Update AlfrescoSDK to 8571d0ea8b