Fix file name handling on MS-Windows 9X.

Fix file name handling on MS-Windows 9X.

 src/w32.c (maybe_load_unicows_dll): New function.
 src/emacs.c (main) [WINDOWSNT]: Call maybe_load_unicows_dll early
 on, to make sure we can convert file names to and from UTF-8 on
 Windows 9X.  This fixes a failure to start up because Emacs cannot
 find term/w32-win.el.  Reported by oslsachem <oslsachem@gmail.com>.
 src/w32font.c [WINDOWSNT]: Include w32.h.
 (w32_load_unicows_or_gdi32): Call maybe_load_unicows_dll, instead
 of implementing the same stuff.
 Remove now unused g_b_init_is_windows_9x.
 src/w32.h (maybe_load_unicows_dll): Add prototype.

 nt/runemacs.c (ensure_unicows_dll): Don't tell in the message box
 that "emacs -nw" can do without UNICOWS.DLL on Windows 9X.  See
 w32.c:maybe_load_unicows_dll and its callers for the reason.