Revert "The segfault is fixed upstream in the meantime."

It still crashes on travis-ci.org.

This reverts commit a42ba50227ea97e40707ae900ab772f817a7eadd.
Fix test case test_shaders_3.
- uniform variables are optimized out if not used.
- Use better test values.
tabs to spaces
Presume maximum attribute/uniform name length, if not returned by glGetProgramiv.

This works around an issue with the linux nvidia driver.
Fix test case test_shaders_2: Variables are optimized out if not used.
Reactivate test_gluniformmatrix21, since it passes on nvidia drivers.