Handle OS_OBJECT_USE_OBJC=0

The leak was because for targets < 5 CocoaPods added the define `OS_OBJECT_USE_OBJC=0` which made it our responsibility to deallocate `dispatch_queue_t`s.

We now check for OS_OBJECT_USE_OBJC and deallocate the dispatch queue in those circumstances, however I also boosted the minimum iOS deployment target to 6. I think this is reasonable in this day and age.

I kept OS X at 10.7 however, people still want to support 10.7. This means leaks may happen in various components that expect ARC but don’t realize some parts of Foundation require explicit releases etc.