Revert "Convert BGR surface to RGB ones in FormatAlpha."

This reverts commit 71040ee5110aa7a329f096a415e78c53bdd60d9e.
Switch compiler flags around.

The build was failing for me the other way. Hrm.
Optimize SDL_PNGFormatAlpha and make it correct C89.
Allow BGR surfaces, properly this time.
Free the RWops resource properly, if freedst is set.

The correct way to do it is to call SDL_RWclose, not SDL_FreeRW.