Python: Better handling of sensitive functions

This solution was the best I could come up with, but it _is_ a bit
brittle since you need to remember to add this additional taint step
to any configuration that relies on sensitive data sources... I don't
see an easy way around this though :|

python/ql/test/experimental/dataflow/sensitive-data/TestSensitiveDataSources.ql

@@ -40,6 +40,10 @@ class SensitiveUseConfiguration extends TaintTracking::Configuration {
   override predicate isSink(DataFlow::Node node) {
     node = API::builtin("print").getACall().getArg(_)
   }
+
+  override predicate isAdditionalTaintStep(DataFlow::Node node1, DataFlow::Node node2) {
+    sensitiveDataExtraStepForCalls(node1, node2)
+  }
 }
 // import DataFlow::PathGraph
 // from SensitiveUseConfiguration cfg, DataFlow::PathNode source, DataFlow::PathNode sink