add back xmltooling

diff --git a/shibboleth/xmltooling b/shibboleth/xmltooling
new file mode 160000 (submodule)
index 0000000..21ecbfb
--- /dev/null
+++ b/shibboleth/xmltooling
@@ -0,0 +1 @@
+Subproject commit 21ecbfb331400c6acb087b809dfa07dc20d5a6fb