Screen-Over implementation for software renderer.

This fixes the ground for both Virtua Fighter 2
and Toshiden.

git-svn-id: https://yabause.svn.sourceforge.net/svnroot/yabause/trunk@3032 d7be59e3-070e-4b9a-85a1-4646befae34d
Implementation of VDP1 shadows.

This fixes the shadows in Mystaria battles.

git-svn-id: https://yabause.svn.sourceforge.net/svnroot/yabause/trunk@3033 d7be59e3-070e-4b9a-85a1-4646befae34d