Merge branch 'pr/2546' into master.

https://github.com/scipy/scipy/pull/2546
MAINT: clean up comments/commented-out code in distributions.py; some PEP8 fixes.
MAINT: enable rdist._cdf, making it a lot faster.  Closes gh-1285.

Issue for hyp2f1 that is worked around is discussed in gh-1561.
ENH: add central moment methods to invweibull and loglaplace distributions.

Faster, more accurate and removes a warning generated by the distribution fit
test for invweibull.
TST: speed up stats tests some more, and add run_module_suite to each test file