Sufficient, but not always necessary.
Add borderClip to damage on creation so that clients needn't guess.
Fix API to FbDots functions to make PolyPoint work with screen_x/screen_y
    offsets
Add debugging code to make sure no pictures are left pointing at freed
    pixmaps. "Can't" happen, but it did once.
Change KdOffscreenArea structure to eliminate separate private structure,
    eliminate the ScreenPtr, change from doubly linked to singly linked
    list.
Don't damage BackgroundNone windows on PW_BACKGROUND. Re-clip damage to
    borderClip in DamageSubtract.