Don't raise a property name collision if the colliding alias and ndb properties aren't defined on the same level of the MRO

[dhermes]

Don't raise a property name collision if the colliding alias and ndb properties aren't defined on the same level of the MRO

This doesn't occur always, but

from google.appengine.ext import ndb
from endpoints_proto_datastore.ndb import EndpointsModel

class SomeModel(EndpointsModel):
  other_prop = ndb.StringProperty('id')

results in the following exception

Traceback (most recent call last):
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/devappserver2/python/request_handler.py", line 151, in handle_interactive_request
    exec(compiled_code, self._command_globals)
  File "<string>", line 4, in <module>
  File "/Users/dhermes/endpoints-proto-datastore/examples/simple_get/endpoints_proto_datastore/ndb/model.py", line 459, in __init__
    cls._FixUpAliasProperties()
  File "/Users/dhermes/endpoints-proto-datastore/examples/simple_get/endpoints_proto_datastore/ndb/model.py", line 480, in _FixUpAliasProperties
    raise AttributeError(PROPERTY_COLLISION_TEMPLATE % (attr_name,))
AttributeError: Name conflict: id set as an NDB property and an Endpoints alias property.

while

from google.appengine.ext import ndb
from endpoints_proto_datastore.ndb import EndpointsModel

class SomeModel(EndpointsModel):
  id = ndb.StringProperty()

does not result in an exception.