Try to fix Travis slow down. This also make sure to don't have speed regression.

theano/gof/destroyhandler.py

@@ -395,7 +395,7 @@ class DestroyHandler(toolbox.Bookkeeper):  # noqa
         fgraph.destroyers = get_destroyers_of
 
         def has_destroyers(protected_list):
-            if not self.stale_droot:
+            if self.algo != 'fast':
                 droot, _, root_destroyer = self.refresh_droot_impact()
                 for protected_var in protected_list:
                     try: