Use an unsafe self reference in -[RACSubscriber init]

A weak reference is unnecessarily expensive, and this disposable is
guaranteed to be used before the captured object disappears.
Reference disposables directly in -didSubscribe…

Avoids any need for weak references, since the RACSubscriber is no
longer being captured.
Merge pull request #1500 from ReactiveCocoa/unsafe-subscriber-ref

Use an unsafe self reference in -[RACSubscriber init]
Fix retain cycle in -didSubscribeWithDisposable:

otherDisposable can't create a cycle with itself, just in case
it's never disposed of.
Merge pull request #1501 from ReactiveCocoa/fix-subscriber-disposable-cycle

Fix retain cycle in -didSubscribeWithDisposable:
Merge branch 'master' into merge-master-in-legacy

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/RACDynamicSignal.m
	ReactiveCocoaFramework/ReactiveCocoa/RACSubscriber.m
	ReactiveCocoaFramework/ReactiveCocoaTests/RACMulticastConnectionSpec.m
	ReactiveCocoaFramework/ReactiveCocoaTests/RACPropertySignalExamples.m
	ReactiveCocoaFramework/ReactiveCocoaTests/RACSignalSpec.m
Merge branch 'merge-master-in-legacy' of github.com:ReactiveCocoa/ReactiveCocoa into merge-master-in-legacy