OpenGL output + minor tweaks

The big thing here is OpenGL code from bsnes plus a selection of filter shaders from that same project. Even with the unfortunate software blit to convert the surface to 32bpp, this code still gets twice the FPS compared to x4 software scaling and the filters don't slow it down.

Michal has added -lopengl32 to the gitbuilder makefile so automatic builds should be OK.

Also in this PR:
- further deferred palette update until the first new update to the screen (actually until the next flip after the next getSurface() call); it seems to fix the mess when a base is being attacked, at least.
- added the RLE acceleration flags to surfaces; not sure it's doing anything tho
- pulled in the code to set display base width and base height from the config file; it's pretty trivial