python: fixup, test

python/ql/test/library-tests/frameworks/tornado/taint_test.py

@@ -63,7 +63,7 @@ def get(self, name = "World!", number="0", foo="foo"):  # $ requestHandler route
             request.headers["header-name"], # $ tainted
             request.headers.get_list("header-name"), # $ tainted
             request.headers.get_all(), # $ tainted
-            [(k, v) for (k, v) in request.headers.get_all()], # $ tainted
+            [(k, v) for (k, v) in request.headers.get_all()], # $ MISSING: tainted
 
             # Dict[str, http.cookies.Morsel]
             request.cookies, # $ tainted