Rotate n relocate

[rautonkar]

Relocating buffers into bss if desired.

Added simple changes which should prevent malloc if pointer is already assigned during DG_Init. This applies to both I_VideoBuffer and DG_ScreenBuffer.

Added in code to rotate the buffer

Clockwise buffer rotation is disabled by default. Can be turned on by enabling the preprocessor in the i_video.c file or by adding in a compiler preprocessor flag ROTATE_SCREENBUFFER.
By manipulating at cmap; you can bypass the need to create a third buffer and a copy operation which will degrade performance. The code is not tested at higher resolutions.

[ozkl]

I was goint to merge this but when I tested the code, it gave me this even in 320x200 resolution:

I think this would add value to doomgeneric as it could be useful in some embedded environments.