Bug #948 - Remove texture rectangle support
* clutter/clutter-feature.c:
* clutter/clutter-feature.h:
* clutter/clutter-texture.c:
* clutter/cogl/gl/cogl.c:
* clutter/glx/clutter-glx-texture-pixmap.c:
Remove support for GL_TEXTURE_RECTANGLE_ARB (now using just regular
2D textures, with optional npots extension). Simplifys code, + makes
mipmap & shader support much more sane.