[Piglit] to-do item: clean up GL error checks

[Brian Paul]

If someone's looking for something simple to do in piglit...

There's about 150 instances of this in the tests:

assert(glGetError() == 0);

I think that quite a few of them should be replaced with:

if (!piglit_check_gl_error(GL_NO_ERROR))
    fail;

Some seem to be development sanity checks but some seem to be 
intentional GL error checks.

I also saw some of this (in the fbo tests, for example):

	err = glGetError();
	if (err != GL_NO_ERROR) {
		printf("Unexpected GL error state 0x%04x\n", err);
		piglit_report_result(PIGLIT_FAIL);
	}

Again, we could use piglit_check_gl_error().

That would be a good clean-up project for someone who wants to get 
into piglit or has some spare time.

-Brian