Correct thread unsafe code when printing a too large float value.

  This was left from the original implementation when multiple threads
were not supported. Now it is unsafe to have a temporary not reachable
if another thread may call gc.
Add the NeHe example rending a video to a texture

  In the example it just reads from /dev/urandom; actual contents
(nor how to convert the frame to a rgb image) are not the point of
the example, but how to put it in an OpenGL texture.