Peter M. Groen / openbr

Updated threading for stream, updated waiting for parallel work to finish

Release a thread from the global thread pool whenever we wait for a parallel
job to finish. This means we don't waste one of the global thread pool's
threads, and can maintain full CPU utilization.

Change the threading model used in stream slightly, generally as a given frame
is processed a single thread will attempt to continue working on it as it
progresses through the processing stages. Frames will be queued if a single
thread stage is already occupied when the thread gets there.

This update can be used with a large total number of frames being processed
without, while still maintaining relatively smooth playback by giving later
stages higher priority in the qt thread pool.

Check for a NULL transform in CacheTransform::init
How can you doubt me?

Conflicts:
	openbr/plugins/meta.cpp

Update multi-threading model used by stream, and some gui tweaks

Also, add FPSCalc, and FPSSynch to calculate the frequency of frames passing
through a stream, and to slow down processing to a specific frame rate (note:
does not work particularly well), respecively.

Rather than having threads at each stage block, and wait for input, use the
global thread pool to only execute stages when they have input.