[algorithm][loop] The validate method now returns a tuple

The tuple should contain a:
- boolean for success or failure
- dictionary with the data to return to the algorithm

beat/backend/python/algorithm.py

@@ -287,7 +287,13 @@ class Runner(object):
         if not self.prepared:
             raise exc("Algorithm '%s' is not yet prepared" % self.name)
 
-        return loader.run(self.obj, 'validate', self.exc, result)
+
+        answer = loader.run(self.obj, 'validate', self.exc, result)
+
+        if not isinstance(answer, tuple):
+            raise exc("Improper implementation: validate must return a tuple")
+
+        return answer
 
 
     def __getattr__(self, key):