Changes:

FIxed a blitter bug in SDL_Blit.h.  This has been upstreamed; the change
should no longer be needed when SDL 1.2.6 is released.

Disable "g" optimizations in the blitter; an optimizer bug (or some obscure
blitter bug) shows up in VC7 without that.  This has been sent upstream
and I'm awaiting a response.

SDL builds "SDLd.dll,lib" and "SDLmaind.dll,lib" for debugging, and we link
against it conditionally.  This makes debugging a lot easier.  (Sent upstream,
awaiting reply.)

Libraries are output to lib/ instead of VisualC/SDL{main,}/{Debug,Release}.
That's where it is by default, so that's where the build puts it.  (Sent
upstream, awaiting reply.)

SDL DLLs are output to ../.. (the top-level SM directory).  That's where SM
is, so you don't have to copy the DLL every time you change something
in the SDL source (and possibly forget).  SDLmain isn't, since we don't actually
use that.  Not sent upstream, of course.

Turned off incremental links, since it ends up in the SM directory, and it's
just more clutter--the SDL links really fast anyway.

** Important:
Be careful about runtime linkage.  I've changed all links to use
multithreaded static; this keeps things from pulling in the VC7
runtimes, but adds a bit to each DLL.  The DLL itself is about 300k;
I'm not sure if it's a redistributable.  Also, SDL_image has a debug
version that links against the SDL debug.  I havn't actually had to
debug it yet, so it's not really important; however, if that's not
done then it'll pull in both the debug and non-debug version of the
SDL (one for SM, one for image), which is ugly and might cause problems.

-glenn
