TST: add tests for numpy version string comparison utility.
ENH: implement lib._version.NumpyVersion which compares numpy version strings.
BUG: incorrect check in NumpyVersion for dev versions.
TST: convert all numpy version checks to use NumpyVersion.
BUG: fix comparison of NumpyVersion's 1.9.0 and 1.10.0.  Closes gh-2998.
BUG: NumpyVersion object: ``__cmp__`` not supported by python 3.x
Merge pull request #3170 from rgommers/version-compare

Fix numpy version checks