Makes some cases less consistent (and some convenience shortcuts
impossible), but goes well with the attitude "don't use pointer when it
can't be null".
* Older GLSL doesn't have texelFetch() and related things, working
around it by using classical texture() and normalized floating-point
coordinates. But that needs to have Texture::imageSize() passed,
which is not available in OpenGL ES, thus the user must specify it
explicitly there. On desktop OpenGL that parameter is ignored.
* Older GLSL doesn't have gl_VertexID, thus vertex buffer must be
created and vertex data passed expliticly.
* GLSL ES 2.0 doesn't have one-component texture format and
TextureFormat::Luminance probably isn't renderable anywhere, thus
TextureFormat::RGB should be used, although it is inefficient.
* Checking for framebuffer completeness, if not complete, nothing is
done.
* Re-eabled building of TextureTools library in all ES PKGBUILDs.
Removed unneeded member variables, removed wrong assertions and wrong
documentation (most of the state they were fobidding is actually valid).
Retrieving shader log with full length, properly printing non-error
messages to debug output.
Each shader must now be compiled explicitly using compile(), which is
slightly better for the user as it is possible to check compile status
instead of having it weirdly hidden inside attachShader(). link() now
also returns linking status.
Vladimír Vondruš