Emulate undocumented behavior when reading/writing to PPU address $2007 when not in vblank. This fixes the garbage on screen when scrolling vertically in The Young Indiana Jones Chronicles.

Credit for this goes to NESDev board members James, who originally figured out the undocumented behavior, and plasturion, who initially implemented this in Nestopia. http://forums.nesdev.com/viewtopic.php?t=6401