prefer to use ldns-config to find libldns

Should fix bz#2603 - "Build with ldns and without kerberos support
fails if ldns compiled with kerberos support" by including correct
cflags/libs

ok dtucker@

configure.ac

@@ -1475,17 +1475,29 @@ LDNS_MSG="no"
 AC_ARG_WITH(ldns,
 	[  --with-ldns[[=PATH]]      Use ldns for DNSSEC support (optionally in PATH)],
 	[
-        if test "x$withval" != "xno" ; then
-
-			if test "x$withval" != "xyes" ; then
+	ldns=""
+	if test "x$withval" = "xyes" ; then
+		AC_PATH_TOOL([LDNSCONFIG], [ldns-config], [no])
+		if test "x$PKGCONFIG" = "xno"; then
 			CPPFLAGS="$CPPFLAGS -I${withval}/include"
 			LDFLAGS="$LDFLAGS -L${withval}/lib"
+			LIBS="-lldns $LIBS"
+			ldns=yes
+		else
+			LIBS="$LIBS `$LDNSCONFIG --libs`"
+			CPPFLAGS="$CPPFLAGS `$LDNSCONFIG --cflags`"
+		fi
+	elif test "x$withval" != "xno" ; then
+			CPPFLAGS="$CPPFLAGS -I${withval}/include"
+			LDFLAGS="$LDFLAGS -L${withval}/lib"
+			LIBS="-lldns $LIBS"
+			ldns=yes
 	fi
 
+	# Verify that it works.
+	if test "x$ldns" = "xyes" ; then
 		AC_DEFINE(HAVE_LDNS, 1, [Define if you want ldns support])
-            LIBS="-lldns $LIBS"
 		LDNS_MSG="yes"
-
 		AC_MSG_CHECKING([for ldns support])
 		AC_LINK_IFELSE(
 			[AC_LANG_SOURCE([[
@@ -1502,8 +1514,7 @@ int main() { ldns_status status = ldns_verify_trusted(NULL, NULL, NULL, NULL); s
 					AC_MSG_ERROR([** Incomplete or missing ldns libraries.])
 				])
 	fi
-    ]
-)
+])
 
 # Check whether user wants libedit support
 LIBEDIT_MSG="no"
@@ -5083,6 +5094,7 @@ echo "                 Smartcard support: $SCARD_MSG"
 echo "                     S/KEY support: $SKEY_MSG"
 echo "              MD5 password support: $MD5_MSG"
 echo "                   libedit support: $LIBEDIT_MSG"
+echo "                   libldns support: $LDNS_MSG"
 echo "  Solaris process contract support: $SPC_MSG"
 echo "           Solaris project support: $SP_MSG"
 echo "         Solaris privilege support: $SPP_MSG"