* Store the number of frames per sprite2 run in the spr2frames struct.
* Reintroduce P_GetModelSprite2, to allow for the sprite2 defaulting system to be used to full advantage even in GL.
* Instead of splitting the SUPER and normal SPR2 stuff within the same cell of the struct, have them exist in different cells just like in the "normal" sprite2 structs.
* Allow for just providing spr2 frames in order without specifying which "normal" sprite2 frame it's supposed to replace.
Also:
* Fix FF_VERTICALFLIP-ignoring regression.
* Fix whitespace adjustment in win_dll.c
* Remove bracket in P_GetSkinSprite2 because I realised it was extraneous while making sure P_GetModelSprite2 worked with it.
Only use glCopyTexImage2D when first creating the screen texture, use glCopyTexSubImage2D anytime after that as it does not define a new texture each time.
Flushing of the screen textures has been implemented for when the screen size changes (so that the screen textures don't stay at a wrong size) and the game is closed, I believe they would leave a memory leak before.
