Make OSX test application more idiomatic and add rendering callback
Use libc++ inspired clock instead of the deprecated AbsoluteToNanoseconds

This also makes the clang static analyzer happy (it complained about
uninitialized fields in the AbsoluteTime struct)
Properly bridge CF object so ARC can deal with it
Add NULL checks and assertions to fix clang static analysis problems

Also remove an unused variable from obs-encoder.c (via clang static
analysis)