add mavlink submodule check script

The script checks if the mavlink submodule is up to date

Tools/check_submodules.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+STATUSRETVAL=$(git status --porcelain | grep -i "M mavlink/include/mavlink/v1.0")
+if [ "$STATUSRETVAL" == "" ]; then
+	echo "checked mavlink submodule, correct version found"
+else
+	echo "mavlink sub repo not at correct version. Try 'git submodule update'"
+	exit 1
+fi
+
+exit 0