win32 updates (from <Someone>)

- restructured Install.nt quite a bit. It now contains instructions
to build a graphical nethack using NMAKE, too. I merged
the instructions for command line builds, and separated the IDE
build; that made more sense to me. It is shorter, too.
- added some lines to all Makefiles so they now build
NetHackW.exe when GRAPHICAL is "Y", and NetHack.exe
otherwise. I espacially did not test this on Borland.
Previously, the makefiles would always build NetHack.exe.
- changed the IDE files to build NetHackW.exe instead of
nethackw.exe. This is only cosmetic, but consistent with the
other executable.
- made a small change to pcmain.c, as the MinGW linker
cannot decide between main() and WinMain() when both are
present, as explained in <Someone>'s original
message. (I used a #ifndef instead of comments ;-)
The MinGW graphical build indeed seems to work.

sys/winnt/Makefile.bcc

@@ -92,7 +92,11 @@ libsmt  = $(bcclib)\cw32mt.lib $(bcclib)\import32.lib
 #  Set the gamedir according to your preference.  
 #  It must be present prior to compilation.
 
+!IF "$(GRAPHICAL)" == "Y"
+GAME    = NetHackW                # Game Name
+!ELSE
 GAME    = NetHack                 # Game Name
+!ENDIF
 GAMEDIR = ..\binary               # Game directory
 
 #