abuild-sign: reformat error output

abuild-sign.in

@@ -79,13 +79,15 @@ if [ $# -eq 0 ]; then
 fi
 
 if [ -z "$privkey" ]; then
-	echo "No private key found. Use 'abuild-keygen' to generate the keys"
-	echo "Then you can either:"
-	echo " 1. set the PACKAGER_PRIVKEY in $abuild_userconf"
-	echo "    (Note that 'abuild-keygen -a' does this for you)"
-	echo " 2. set the PACKAGER_PRIVKEY in $abuild_conf"
-	echo " 3. specify the key with the -k option"
-	echo ""
+	cat >&2 << __EOF__
+No private key found. Use 'abuild-keygen' to generate the keys.
+Then you can either:
+  * set the PACKAGER_PRIVKEY in $abuild_userconf
+    ('abuild-keygen -a' does this for you)
+  * set the PACKAGER_PRIVKEY in $abuild_conf
+  * specify the key with the -k option to $prog
+
+__EOF__
 	exit 1
 fi