Print an error message and exit with a non-zero code when we hit the timeout. This makes it clear when a test fails due to a timeout. On Darwin, run `sample` on the target process first, so that the failure includes some information about what the test was doing when the timeout occurred.
The `__future__` we relied on is now, where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):
* absolute_import
* print_function
* unicode_literals
* division
These import statements are no-ops and are no longer necessary.
