Un-separate synchronous vs asynchronous in interface; call operation blo...

[jacobjennings]

...ck directly in synchronous case to guarantee completionBlock called before returning

waitUntilFinished was not reliable because it doesn't guarantee the
completionBlock being called, only the operation being completed. I confirmed this by noting that the resultImage in the operation block was never nil, while the completion block was being called with a nil image.

Let me know what you think of the interface change.

[JaviSoto]

You're right, waitUntilFinished isn't safe. But I like keeping the interface more decoupled from the implementation details, and that's why I liked having two methods. I believe the waitUntilFinished issue could be solved by using dispatch_group_enter and dispatch_group_wait.