Fix #129: use transaction ID from connection's own transaction.
Fix #131:  return datetime w/ UTC zone.
Don't pass transaction ID to connection.rollback_transaction().

Feedback from @dhermes.
Removing keyword "type" from storage.acl.
Using more descriptive entity_type instead of type_.
Merge pull request #180 from tseaver/129-rollback_using_connection_xact

Fix #129: use transaction ID from connection's own transaction.
Merge pull request #156 from dhermes/fix-overloaded-keyword

Removing overloaded global "type" from storage.acl.
Merge pull request #181 from tseaver/131-return_dateimtes_w_utc_zone

Fix #131:  return datetime w/ UTC zone.
Updated datastore.entity with pyfmt.
Updated datastore.entity by hand until fully passed pep8.
Resolved all pylint errors in datastore.entity.

Pylint errors were:
  C: 90, 0: Line too long (82/80) (line-too-long)
  W: 67, 4: __init__ method from base class 'dict' is not called (super-init-not-called)
  C:138, 4: Invalid argument name "pb" (invalid-name)
  E:177,43: Instance of 'Entity' has no 'to_protobuf' member (but some types could not be inferred) (maybe-no-member)
  E:191,19: Instance of 'Entity' has no 'to_protobuf' member (but some types could not be inferred) (maybe-no-member)
  E:196,27: Instance of 'Entity' has no 'is_partial' member (but some types could not be inferred) (maybe-no-member)
  E:202,18: Instance of 'Entity' has no 'path' member (but some types could not be inferred) (maybe-no-member)
  E:216,51: Instance of 'Entity' has no 'to_protobuf' member (but some types could not be inferred) (maybe-no-member)
  E:221,38: Instance of 'Entity' has no 'path' member (but some types could not be inferred) (maybe-no-member)
  R: 24, 0: Too many public methods (25/20) (too-many-public-methods)
  W: 18, 0: Unused import datetime (unused-import)