Update PyMongo requirement to master@0b831cb8.
Introduce MotorCommandCursor.

Mirrors PyMongo 2.7's separation of find() cursors from aggregate(), etc. cursors.
More reliable tests.
Clearer conditional.
Fake CommandCursor for synchrotest.
Skip test_cursor_transfer in synchrotest.
squash
Import order.
Fix ssl_match_hostname in synchrotest.
Implement parallel_scan, MOTOR-18.