Make traitlets notify check more robust against classes redefining equality and bool

Before this change, numpy arrays caused problems since comparing two numpy arrays returns an array of truth values, rather than a single truth value.  This change guards against redefining the semantics of comparison by notifying on a trait change if the equality comparison returns anything other than an explicit True value.

IPython/utils/traitlets.py

@@ -372,11 +372,13 b' class TraitType(object):'
         old_value = self.__get__(obj)
         obj._trait_values[self.name] = new_value
         try:
-            notify = (old_value != new_value)
+            silent = bool(old_value == new_value)
         except:
             # if there is an error in comparing, default to notify
-            notify = True
-        if notify:
+            silent = False
+        if silent is not True:
+            # we explicitly compare silent to True just in case the equality
+            # comparison above returns something other than True/False
             obj._notify_trait(self.name, old_value, new_value)
 
     def _validate(self, obj, value):