Add a pruned down test which shows a white box

This adds a very simple test which just draws a texture.  This is a pruned down version of [a signal test I found in JPCSP's repo] (http://code.google.com/p/jpcsp/source/browse/trunk/demos/src/GEtest/main.c).

It shows a white box on the PSP, but in PPSSPP it shows black (even if I add a delay.)

The original test had signal commands, as soon as I remove those it stops displaying anything.  With the signals it displays stuff, but wrong colors (the signal handler changes the clut in the original test.)

Anyway, I think this test is still valid.

-[Unknown]