need a workaround for missing distribution classes after scipy refactoring.
They are back in 0.14.1, AFAIK
see #1311 (comment)
and also in appveyor testing PR #1800
TST error with scipy 0.14 location distribution class, closes #1801 c…
they are not back in scipy 0.14.1 (I confused it with adding rvs_frozen back on the path)
see also #1803