Add some missing SDL2 includes when not using sdl2-config.


git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@1017 af15c1b1-3010-417e-b628-4374ebc0bcbd
Load world and brush models into a VBO, and draw it in batches in R_DrawTextureChains_Multitexture. Uses the same immediate mode code as before if VBOs are not available, or if "-novbo" used at the command line. I only touched R_DrawTextureChains_Multitexture because it's usually the main bottleneck aside from alias model rendering.

This seems to help fps a fair bit on maps with a lot of world polys like jam2_tronyn. Tried on a few computers with intel and nvidia gpus, windows, mac os, linux, and there's always at least some fps improvement. Best case was 70fps -> 96fps on jam2_tronyn, on OS X + nvidia 650gt.

Interested to hear how this works for amd gpu's, just do a timedemo with and without "-novbo".

Only downside is I had to disable the fast path in Vid_Toggle_f() because at least with SDL1, the vbo no longer works after a toggle. So as a result, fullscreen toggles with alt-enter are slightly slower.

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@1018 af15c1b1-3010-417e-b628-4374ebc0bcbd