Added test for subscribers retaining disposed disposables.
Abuse the fact -didSubscribeWithDisposable: is only ever passed compound disposables to change the signature.
Fixed RACSubject and RACSubscriber retaining disposed disposables.
Changed the expectation to asynchronous since the setting is asynchronous.
Documented the asynchronicity of the NSUserDefaults channel.
Merge pull request #1128 from ReactiveCocoa/subscribers-retaining-disposed-disposables

Subscribers retaining disposed disposables
Nicer wording.
Merge pull request #1150 from ReactiveCocoa/fix-nsuserdefaults-test

Document the NSUserDefaults' channel's asynchronicity.
Merge branch 'master' into fix-kvowrapper-test

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/RACChannel.m
	ReactiveCocoaFramework/ReactiveCocoa/RACPassthroughSubscriber.m
	ReactiveCocoaFramework/ReactiveCocoa/RACSubject.m
	ReactiveCocoaFramework/ReactiveCocoa/RACSubscriber.h
	ReactiveCocoaFramework/ReactiveCocoa/RACSubscriber.m
	ReactiveCocoaFramework/ReactiveCocoaTests/RACSubscriberExamples.m