General emulation flaws
=======================

* Layer A turning off is not supported in left-right direction when Window is
  used (however window *is* done correctly at a higher priority, so maybe
  nobody will ever notice). (is there a game that uses this??)

* Interlace mode doesn't support windows (is there a game that uses this
  so I can test it??)

* The main loop in reg68k checks for events every block, I mean, duh, why
  aren't I calculating how many clocks UNTIL the next block, executing that,
  and THEN doing something. (two branch instructions per block could be
  saved here maybe...)

Specific game bugs
==================

Sonic 2
-------
When in interlace mode, there is supposed to be a one-cell gap in the middle
that is solid blue.  In Generator's emulation, layer A trees and sprites
appear on top, this is not the case on a real Mega Drive.
The title screen also appears not as it should, with Sonic and Tails appearing
on top of the logo.

Sonic 3D
--------
The trap-door under the portal looking thing appears on top instead of
behind the main Sonic sprite.

yuuyuu
------
After logos, blank screen and music plays, nothing happens.

Wolfchild
---------
Layers are corrupt - this is due to a routine at e1b80.  This is a very
simple loop that seems to copy 120 bytes at c000, then 120 bytes at c004
etc... really bizaare why it would do that.  DGen does the same as Generator,
KGen and Genecyst gets it right.
e1a8a
  e1a8e->e1b42
           e1b7c->e1b80
                    e1ba8->e2ed4
                  e1bc0

Road Rash 2
-----------
Screen corruption

Out Run
-------
This is bizaare - with the correct number of CPU clocks per line, you get 
screen corruption on the road, but with less or more CPU clocks, the screen
corruption goes away...

Alien Storm
-----------
When you enter a level there are a series of dots in the title screen, this
is due to a bug I introduced in CRAM code for version 0.14.  Must fix this :)
