Rename test directory and add comment to clarity on the purpose of splitting them.

Author: joefarebrother

python/ql/test/query-tests/Security/CWE-113-HeaderInjection/Tests2/HeaderInjection.expected renamed to python/ql/test/query-tests/Security/CWE-113-HeaderInjection/Tests2-with-wsgi-validator/HeaderInjection.expected

@@ -1,3 +1,5 @@
+# These tests use a wsgi validator; so are split into a separate directory from the other tests since the models only check for the presence of a validator in the database. 
+
 from wsgiref.simple_server import make_server 
 from wsgiref.headers import Headers
 from wsgiref.validate import validator