Detect the presense of libgsasl library.

+dnl This file is part of GNU mailutils.
+dnl Copyright (C) 2003 Free Software Foundation, Inc.
+dnl
+dnl GNU Mailutils 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, or (at your option)
+dnl any later version.
+dnl 
+dnl GNU Mailutils 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 GNU Mailutils; if not, write to the Free Software
+dnl Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA  
+dnl
+AC_DEFUN(MU_CHECK_GSASL,
+[AC_CACHE_CHECK([whether to use GNU SASL library],
+                 [mu_cv_lib_gsasl],
+ [if test "x$mu_cv_lib_gsasl" = x; then
+   cached=""
+   mu_cv_lib_gsasl=no
+
+   AC_ARG_WITH(gsasl,
+     AC_HELP_STRING([--with-gsasl], [use libgsasl for SASL authentication]),
+     [case $withval in
+      yes|no) wantgsasl=$withval;;
+      *) AC_MSG_ERROR(bad value for --with-gsasl: $withval);;
+      esac],
+     [wantgsasl=no])
+
+   if test $wantgsasl = yes; then
+     AC_CHECK_HEADER(gsasl.h,
+                     [:],
+                     [wantgsasl=no])
+
+     if test $wantgsasl != no; then
+       save_LIBS=$LIBS
+       AC_CHECK_LIB(gsasl, gsasl_init,
+                    [mu_cv_lib_gsasl=-lgsasl],
+                    [mu_cv_lib_gsasl=no])
+       if test $mu_cv_lib_gsasl != no; then
+         LIBS="$LIBS $mu_cv_lib_gsasl"
+         AC_TRY_RUN([
+#include <gsasl.h>
+
+int
+main()
+{
+  return gsasl_check_version ("$1") == (char*) 0;
+}],
+                    [:],
+                    [mu_cv_lib_gsasl=no],
+                    [mu_cv_lib_gsasl=no])
+       fi
+       LIBS=$save_LIBS
+     fi       
+   fi
+  fi])
+ if test $mu_cv_lib_gsasl != no; then
+   GSASL_LIBS=$mu_cv_lib_gsasl
+   ifelse([$2],,,[$2])
+ fi])
+