The methods failure_message_for_should and failure_message_for_should_not
have been updated to failure_message and failure_message_negated respectively.
Alias to the old methods to remain backwards compatibility with RSpec 2.
The "flashes" instance variable that lives within FlashHash has changed
in Rails 4. I have added a shim to get the proper name.
Additionally, the set_the_flash matcher will dup the flash hash for the
controller on which it operates. As #dup does a shallow copy we need to
make sure to also copy the instance variables within the flash hash when
we do this. The Rails 4 version of FlashHash has an extra @discard
variable unlike the Rails 3 version so we make sure to copy that.
Christopher Chow