Multi-head and full-screen

[Mr Flibble]

Overture: Penumbra messes up my monitor settings, failing to correctly restore the previous settings on exit: one is left on, the other is switched off.

I note that SDL is used. 1.2 doesn't properly handle multiple monitors.

I like to have both monitors on even while playing games since I can leave things which I'm keeping an eye on visible on the other monitor. As things stand, I cannot do this and I have to move windows back afterwards. (There are other issues too, but I'll address those separately.)

The game really needs a windowed mode.