Making wine default to the Mac Driver on OS X

[Vincent Povirk]

Maybe we could just skip loading the x11 driver is DISPLAY is unset.
It brings some logic into the driver logic that doesn't really belong
there, but it seems like a reasonable optimization and in practice
would work the way Alexandre wants even when the x11 libraries are as
spectacularly broken as they are on OS X 10.8.

> Wayland isn't here now, but it seems like when it comes it may bring similar
> issues.

For the record, I would argue that wayland should be ahead of x11 in
the default load order, once it's decided that a wayland driver is
ready. Usually, a rootless X server will be available in wayland for
compatibility reasons, and the reverse is not true. And one could use
a similar approach to X11 to make loading the wayland driver fail.

That said, I'm not sure controlling this with an environment variable
that's going to impact other programs is a good idea. Unsetting the
wayland display would mean that any other processes Wine starts
couldn't use that display either. So the only way to do this for Wine
only is still to mess with the registry. If this is just to make a
quick/temporary change from the command line then that's OK, but if so
we shouldn't be using it to implement settings in our Mac product.