An MSVC8 patch to GS_8_1X

Igor,

> I made it compiling with a partial port of your old patch.
> I skipped things that I can't understand in few minutes.
> Please review and improve what you find useful.

It looks like you included all except for
1. Automatically setting the MSVC_VERSION based on the version of 
nmake.
2. Pre-compiled header changes.  The precompiled header code was 
added after the 8_1X branch by you.  I made minor changes to this for 
MSVC8.  So omitting these is Ok unless you also want to port your 
revision 1.16 msvccmd.mak changes.

The changes look Ok, but I haven't tested them.