ENH: stats: Rewrote stats.obrientransform:

* Vectorized and simplified the computation.  For largeish arrays,
  this gives up to 60 times speed improvement.
* Copy-edited the docstring, and added 'References' and 'Examples'.
* `TINY` changed from 1e-10 to `np.sqrt(np.finfo(float).eps)`.
* Added another test.
BUG: stats: make sure obrientransform doesn't crash using numpy 1.5.x when the shapes of the arguments are not all the same
DOC: stats: Improve the example in the obrientransform docstring to show passing the results to f_oneway
Merge pull request #2631 from WarrenWeckesser/stats-obrientransform

ENH: stats: Rewrote stats.obrientransform: