REF: ensure O(N log N) when using fft for acf

The numpy implementation will fall back to a O(N**2) version of the fft
in cases where it cannot factorize the array length, which can be a
increase in runtime of several order of magnitude. This uses the
_next_regular function from scipy to ensure that we always use array
lengths for which fftpack is optimized.
TST: add test for _next_regular

also copy the test for _next_regular from scipy
ENH: accept non-int definitions of cluster groups
ENH: Option to avoid "center" environment.
ENH: use np.unique for indexing clusters
ENH: using human-readable group names instead of integer ids in MultiComparison
added file that got left behind
Put back an import that my IDE incorrectly flagged as unused
Added unit test for the group_order parameter of MultiComparison. It also tests the human-readable labels in TukeyHSDResults are in the right order
Expanded docstring of MultiComparison
Added b prefix to test strings
Test coveralls issue removing if, then
Fixed coveragerc to allow anythin in */statsmodels/*
Changes for single coverage run
Merge remote-tracking branch 'remotes/upstream/master' into travis-miniconda
Change test condition for coverage
Fix for missing font warning
Simplification using globals
Marked known fails
Suppressed noise from matplotlib about .matplotlibrc location
Final modifications to simplify coverage choices
Merge pull request #1536 from bashtage/travis-miniconda

BUG: Restores coveralls for a single build
ENH: Silence test output

A simple patch that makes minimal changes to tests that silences almost all output.
Most fixes were simply changing options to not output (e.g. disp=False), and a few
others trapped errors.

A new class was introduced in tools/testing.py that allows general output in a test
to be silenced.  It would be preferred for code to only raise warnings and not simply
print, so that the warning could be captured instead.
ENH: Converted parallel message to warning

parallel_funciton was printing a warning, but not raising one.  Converted to
a ModuleNotAvailableWarning.

Removed the 'catch all' class that was trapping this test.  Catching all text is
generally a bad idea.