Forcibly set SHELL and MAKESHELL to force Make to use

COMMAND.COM as the shell.

msdos/mainmake.v2

@@ -29,6 +29,12 @@
 # make extraclean
 #      Still more severe - delete backup and autosave files, too.
 
+# This gork is required for those who use a Unix-style shell, and
+# have SHELL in the environment pointing to it.  Here we force
+# Make to use COMMAND.COM instead.  This Makefile won't work otherwise.
+override SHELL=/dos/command
+override MAKESHELL=/dos/command
+
 # Generate a full pathname of the top-level installation directory
 top_srcdir := $(subst \,/,$(shell cd))