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Tornado 3 compatibility in async_test_engine
Avoid warning in test_connections_unacknowledged_writes
Try to avoid test_tail_drop_collection timeouts
Improve a comment.
Fix test_stack_context for Tornado 3

From Ben Darnell: "This error has to do with the relationship between the stack_context and the actual stack.  If a coroutine is suspended during the "with" statement that establishes a stack context, then the exit half of the "with" will not be run until after the coroutine is resumed.  You can't do anything asynchronous inside the with block, although you could schedule pool.get_socket on the IOLoop with add_callback."
Test the test utilities
Test the test utilities more
Simplify async_test_engine

Since we're no longer replacing the IOLoop in each test, we have to be more careful when calling functions in order to check their callback handling
Python 2.5 compatibility
Don't throw error if optional callback to MotorReplicaSetClient.open() is omitted
Debug test failure in Jenkins
Continue debugging test failure in Jenkins
Fix race condition in test_motor_grid_file
Goodbye Python 2.5, Tornado has dropped support for you.
Depend on latest PyMongo and Tornado
Test with and without concurrent.Futures backport in Python < 3.2 on Travis
Remove MotorCursor.tail method
Remove MotorCursor.tail method
Remove AssertRaises yield point now that we can use "with self.assertRaises"

Dropping Python 2.5 means we can rely on assertRaises being a context manager,