API: raise if caller supplies both dict and kwargs

I (incorrectly) wrote something like the following:

    api.find({'query': {...}}, keys=['id'], range=[0, n])

and the query was silently ignored, giving totally different
results to what I wanted. fixes #2822

ox/api.py

@@ -52,6 +52,8 @@ class API(object):
 
     def _add_action(self, action):
         def method(self, *args, **kw):
+            if args and kw:
+                raise ValueError('pass either a dictionary or kwargs, not both')
             if not kw:
                 if args:
                     kw = args[0]