New file. Implements MU_ENABLE_SUPPORT defun.

+dnl This file is part of GNU mailutils.
+dnl Copyright (C) 2001 Free Software Foundation, Inc.
+dnl
+dnl This program is free software; you can redistribute it and/or modify
+dnl it under the terms of the GNU General Public License as published by
+dnl the Free Software Foundation; either version 2 of the License, or
+dnl (at your option) any later version.
+dnl
+dnl This program is distributed in the hope that it will be useful,
+dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+dnl GNU General Public License for more details.
+dnl
+dnl You should have received a copy of the GNU General Public License
+dnl along with this program; if not, write to the Free Software
+dnl Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+dnl
+
+dnl MU_ENABLE_SUPPORT(feature, [action-if-true], [action-if-false])
+
+AC_DEFUN([MU_ENABLE_SUPPORT], [
+	pushdef([mu_upcase],translit($1,[a-z],[A-Z]))
+	pushdef([mu_build_files],mu_upcase[_BUILD_FILES])
+	pushdef([mu_cache_var],[mu_cv_enable_]$1)
+	AC_SUBST(mu_build_files)
+	ifelse([$2],,,AC_SUBST(mu_build_dirs))
+	AC_ARG_ENABLE($1, 
+	 [  --disable-]$1[          disable ]$1[ support],
+	 [case "${enableval}" in
+		yes) mu_cache_var=yes;;
+                no)  mu_cache_var=no;;
+	        *)   AC_MSG_ERROR(bad value ${enableval} for --disable-$1) ;;
+          esac],
+         [mu_cache_var=yes])
+
+	if test x"[$]mu_cache_var" = x"yes"; then
+		AC_DEFINE([ENABLE_]mu_upcase,1,[Define this if you enable $1 support])
+		mu_build_files='[$(]mu_upcase[_FILES)]'
+		ifelse([$2],,,$2)
+	ifelse([$3],,,else
+                $2)
+	fi
+
+	popdef([mu_upcase])
+	popdef([mu_build_files])
+	popdef([mu_cache_var])
+])
+
+
+