Apply patch GoogleCloudPlatform#94 manually

It looks like the mapreduce code doesn't properly validate filters of
list properties.

I don't know if this fix is right, but we can try it!

Implements GoogleCloudPlatform#94

Test plan:
Fingers crossed

Auditors: benkraft

Author: csilvers

python/src/mapreduce/input_readers.py

@@ -670,7 +670,12 @@ def _validate_filters(cls, filters, model_class):
             "Property %s is not defined for entity type %s",
             prop, model_class.kind())
 
-      # Validate the value of each filter. We need to know filters have
+       if isinstance(properties[prop], db.ListProperty):
+         # for db.ListProperty validate expect a list, but filter expect
+         # a single value
+         val = [val]
+
+     # Validate the value of each filter. We need to know filters have
       # valid value to carry out splits.
       try:
         properties[prop].validate(val)