Rename QSGCD helpers.

This makes them inline functions, because they are so simple wrappers it's a pain to imagine all those wasted cycles just doing a queue check and calling `libdispatch` function.

Please note I've tried to make ol' `runOnQueueSync` general by using the queue label instead of a `dispatch_specific` value. I'm not sure how that will impact the scanning process though, since we have one queue per scan process (which IMHO is overkill but, well ;-)). I'll do an Instruments run to check how in behaves.