Restore sdl 1.2 to sdl12 interface folder
Initial uncapped framerate implementation
Add cvar capframerate, type CV_OnOff

Default to On
Un-fuck timer code on Windows again
Stub I_GetTimeFrac on other interfaces
Multiply angles directly instead of converting

Fixes the flickery camera issues
Add view contexts

Allows multiple camera renders (2player, skyboxes)
Add common lerp functions

perhaps these can be made inline?
Lerp thing positions
Lerp sector thinkers

Lerping lightlevel and floor/ceiling height for now. Need to lerp flat
offsets at some point too.
Limit water postprocess ripple speed in GL
Uncomment some portal rendering stuff

compiler warnings are scary :(
Lerp T_Scroll-ers