Eliminate the possibility of blocking the caller in SBPerformSelectorAsync by using an NSOperationQueue to dispatch the calls instead of a manual dispatch queue with a blocking semaphore. See https://github.com/iMediaSandboxing/iMedia/issues/49.
Merge branch 'jalkutConcurrencyFix' of https://github.com/redsweater/iMedia into redsweater-jalkutConcurrencyFix

Fix from Daniel Jalkut regarding possibility of deadlock provoked by semaphore