TST: relax test for streamline length

Use almost equal test for alternative streamline length test.
RF: some PEP8 cleanup of test module

Long lines wrapped.
Some empty lines removed.
Specific import of functions to be tested.
Merge pull request #456 from matthew-brett/approx-streamline-tests

MRG: relax threshold for failing test + cleanup

Relax threshold for failing test as suggested by Omar.

Closes gh-455.

Clean up some PEP8 formatting.