Special-case "-r X" where X is [0-9.]+ to mean "-r X-RELEASE".

Tripped over by:	too many people to count
MFC after:	1 month

usr.sbin/freebsd-update/freebsd-update.sh

@@ -284,6 +284,9 @@ config_TargetRelease () {
 	else
 		return 1
 	fi
+	if echo ${TARGETRELEASE} | grep -qE '^[0-9.]+$'; then
+		TARGETRELEASE="${TARGETRELEASE}-RELEASE"
+	fi
 }
 
 # Define what happens to output of utilities