MAINT: rename example file.
STY: removed URL

Linked to: http://www.johndcook.com/blog/2008/09/26/comparing-three-methods-of-computing-standard-deviation/
STY: minor changes to make pep8 happy
ENH: Raise an error when (sufficiently) negative eigenvalues appear.
TST: Adapt test for check on negative eigenvalues.

This is simply replacing the last column of expected (was spurius, ~1e-9)
 with 0s.
TST: Improve comparison of eigenvectors.

It should deal reasonably right in every case.