Limits the damage you take somewhat. Basically, this is intended
to prevent sudden deaths; if it doesn't look like you're dying,
you probably won't suddenly get axed. Of course, this is disabled
in Classic difficulty.
At first I was going to just not bother with the resizing thing, but
then I found out that SDL actually has a scaling function built-in.
So rather than depending on SDL_gfx for this one purpose that never
sees the light of day in practice, I have handed that job over to
that function.
In particular, sizes larger than the background work properly now
(in general; there are of course some things positioned badly still,
but everything updates correctly at any rate).
It's not perfect, but I honestly just can't be arsed to figure out
how to use the Windows API to do the same thing that pwd.h does.
At the very least, Starfighter can now be successfully compiled for
Windows with MinGW simply by defining the "SF_WINDOWS" environment
variable to 1 (or any other non-empty value). The only downside is
that it uses the current working directory to decide where
.config/starfighter should go, meaning it can't be installed into
restricted directories like Program Files.
