Screen/OpenGL-ES: Improve OES extension and core function binding.

Reworked, so it now hopefully works on all OES implementations i can
test, esp. the Ubuntu 13.04 + Nexus-7 implementation for the NVidia
Tegra-3 gpu and drivers.

On ES-2+ try binding the core entry points. On ES-1 try the properly
"OES" suffixed entry-points, but if that fails due to implementation
quirks, retry with non-OES entry points against the ES-2/ES-3 libs.
Screen/ES: Handle ES implementations with only fixed point and line size 1.

If an OpenGL-ES implementation only supports a fixed point diameter or
line width of 1 pixel then skip the size checks and stick to a fixed
1 pixel size for Screen('DrawDots/DrawLine/DrawLines'). This is needed,
e.g., on Tegra-3 of the Google Nexus-7.

Normally we are not lenient if scripts try to select unsupported point/
line sizes, but to get anything going on embedded devices we are more
forgiving here. I guess researchers would note during testing of code
if a varying dot/line size stimulus would show up only with 1 pixel thin
lines or dots, unless the person is really incompetent.
Screen/Waffle: Rebuilt for 64-Bit Octave on Linux with latest changes.