tutorial section 6.2.5 - case insensitive unique emails with db index (app level through validates :email, db level through index+callback hook impl)
tutorial section 6.3.1 - added pw digest field to db
tutorial section 6.3.2 - added several pw tests and has_secure_password method to user model
tutorial section 6.3.4 - added several more pw tests and validation for min length of pw
tutorial section 6.5.1 - added test for downcasing email before persisting user objects
tutorial section 6.5.3 - debugged email regex
merge