New version of the CRT shader from cgwg.

New version of the CRT shader from cgwg.

Changelog:

- More accurate geometry for simulating a spherically curved CRT. Now
  controlled by two parameters: radius of curvature and distance of
  viewer from screen.
- Tilting of the simulated screen.
- Hard border and rounded corners.
- Adjustable overscan.
- Moved most of the parameters to the vertex shader file. See the
  comments at the start of the main function. There are still a few
  #defines that can be toggled in the fragment shader files.
- 3x oversampling of the beam profile. Reduces Moiré patterning at small
  output sizes. This has probably the biggest impact on performance, and
  should be disabled if things become sluggish.

As discussed in this thread:

http://forums.bannister.org/ubbthreads.php?ubb=showflat&Number=74575#Post74575