after executing your script on a clean debian6-19-04-2012.zip installation (just installed "git-core" before to install all certificates for the script), the program /opt/vc/src/hello_pi/hello_triangle doesn't work anymore.
hello_triangle.bin: triangle.c:167: init_ogl: Assertion `state->surface != ((EGLSurface)0)' failed.
I've had a quick look at the code for this, and I'd hazard a guess it's probably because the GPU memory split is set too low.
Try running rpi-update 192 and then run hello_triangle again.
Thanks, with "rpi-update 192" the triangle example worked. Maybe it was some graphics RAM issue? "opt/vc/bin/tvservice -s" on my device says "state 0x120016, 1920x1200 @ 60Hz, progressive" after installing the 19-04 image.
Yeah, if you're using the default 224MB split it's not enough, that's why you see the error.