Name cached signals after class to avoid conflicts with ancestors

Fixes regression added in a3b5485

src/core.py

@@ -367,16 +367,18 @@ def _get_all_signals(cls):
         class.  Newer (most descended) __kaasignals__ will replace older ones if
         there are conflicts.
         """
-        if not hasattr(cls, '__kaasignals_cached__'):
+        cached_attr = '__kaasignals_%s_cached__' % cls.__name__
+        signals = getattr(cls, cached_attr, None)
+        if signals is None:
             signals = {}
             for c in reversed(inspect.getmro(cls)):
                 if hasattr(c, '__kaasignals__'):
                     signals.update(c.__kaasignals__)
 
             # Remove all signals whose value is None.
             [ signals.pop(k) for k, v in signals.items() if v is None ]
-            cls.__kaasignals_cached__ = signals
-        return cls.__kaasignals_cached__
+            setattr(cls, cached_attr, signals)
+        return signals
 
 
     def __init__(self, *args, **kwargs):