Fix #132:  enforce 64-bit ranges on long values for protobuf attrs.
Incorporate feedback from @dhermes.
Merge pull request #182 from tseaver/132-enforce_int64_bounds_for_protobuf_values

Fix #132:  enforce 64-bit ranges on long values for protobuf attrs.
Removing keyword "type" from storage.acl.
Using more descriptive entity_type instead of type_.