Added declaration of -cutOff:.
Added tests for -cutOff:.
Added -cutOff: implementation.
Changed -cutOff: implementation.
Hopefully clearer phrasing.
Got rid of the replay subject.
Renamed the disposables so it's clearer what they refer to.
No need to save this disposable since subjects aren't kept alive by subscribers.
Added some disposal test.
Fixed cut off signal not being disposed as soon as the receiver sends a value.
Renamed -cutOff: to -takeUntilReplacement:.
Changed -takeUntilReplacement: to forward errors from the receiver.
Implement -takeUntilReplacement: without subjects
Expanded the baseline test a bit.
Clarified docs.
Merge pull request #962 from ReactiveCocoa/take-until-replacement-redux

Implement -takeUntilReplacement: without subjects
Merge pull request #957 from ReactiveCocoa/cutoff

-[RACSignal takeUntilReplacement:]