Raise ImportError instead of SystemExit when $DISPLAY is not set, so
regrtest.py will do the right thing.
Add a call to gl.clear() to clear the window before drawing in it.
Add some verbose prints for completeness.
Use gl.v2i() for the coordinates of one of the lines, for a little bit
of variety.
Reduce the time the window is displayed from 5 to 2 seconds.
all the modules attributes are present and creates a small criss-cross
window for 5 seconds (example from the documentation :-) A more
comprehensive test would probably be useful... but maybe overkill.