Improve heuristics to favor panning over copyarea() thanks to pseudocode
from Antonino Daplas <adaplas@hotpop.com>
Signed-off-by: David Eger <eger@havoc.gtf.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>