Fix T37722 - Can't undo deleting a screen layout

Operations on screen and UI stuff is not actually saved in the undo
files/buffers. Therefore, these shouldn't have the flags set for
getting included for undo and in the last operator settings.
Compiler warnings: quiet warnings for gcc4.7x
patch from Sergey
Util Macros: reduce multiple access & conversion for CLAMP/CLAMPIS/ABS
Code Cleanup: pass rectangles as const in insterface files