Merge branch 'develop' of https://github.com/runrev/livecode into feature-threaded_rendering
[[ ThreadedRendering ]] Attempt to make Mac background pattern drawing thread safe.
[[ ThreadedRendering ]] Added global pattern mutex.
[[ ThreadedRendering ]] Add thread-safe inc/dec functions.
[[ ThreadedRendering ]] Ensure MCPattern is ref-count thread safe.
[[ ThreadedRendering ]] Ensure MCGImage is ref-count thread safe.