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
Fixes for 2.6 test failures, replacing astype(str) with apply(str)
ENH: Miniconda-based testing on Travis-CI

Experimental branch that uses miniconda rather than platform
python to test.  Has some advantages in that it is simple to reconfigure
alternative combinations of NumPy, SciPy, Cython and pandas easily,
at least as long as they are provided by Anaconda.
ENH: Alternative travis script that uses Anaconda via Miniconda

Provides an alternative method to test on Travis using Miniconda
that has some advantages from the current system.

- All binary, so no time spent building
- No branching in the execution steps
- Support for up-to-date requirements which are important to test

Also includes a small change to tools/matplotlibrc which changes the backend
to Agg to avoid Tk-related errors on Travis.  Agg is alays available and does not
depend on Qt or another toolkit.

Closes #1500
Changed build configurations to match those discusses in #1523
Fixed config for Python 3.3
Attempt to inspect segfault
Final fixes to remove redundant code from travis config file
Final fixes to remove redundant code from travis config file
Added 4th build configuration

New configuration will always be on the most current versions using Python 2.7
Fixed conda-related issue which allows for no MKL
Added option for cvxopt to Python 2.7, Numpy 1.7 config