use portable hqx code

Not much more to say than what's already been said in PMs and the code submission thread.

Line endings muddle things up a bit - the actual diff in src/CMakeLists.txt is much smaller (use 'git diff -w').

The filters were imported without any changes from googlecode.
The only real code changes are the adaptations in src/gl/textures/gl_hqresize.cpp.