added +once:
clarify docs
yo dawg I heard u like blockz
better docs
test cleanup
Merge branch 'master' into once

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoaTests/RACSignalSpec.m
let's try this again
test the expected scheduler behavior
fix the signal name
new scheduler each time
include the scheduler in the name
fix the return docs
spell out what happens for +immediateScheduler
Merge pull request #501 from ReactiveCocoa/once

Added +once: