warning, volatile canvas, debug of GL functions
make NCPU=<num> rungl   -- for testing
mt_render.c : broadcast with locked mutex
Merge remote-tracking branch 'yura/master'

Conflicts:
	makefile
merge
Fixed (supposedly) mt_render.c

The logic was buggy: after a thread is finished, it did not wait for all
other threads to finish and started to do the work again. Now all
threads and the main thread wait for the whole work done.
Merge branch 'yura'
Fixed __GNU_PREREQ macro

__GNU_PREREQ() is not supported in apple-gcc, changing it to a more
crossplatform way.
FPS handler with gettimeofday()
Improved threading robustness: up to 128 threads
Merge pull request #6 from EarlGray/master

Improved version of multithreading rendering.