RF: better tests of current axis finding algorithm

I didn't understand it myself, so working through with tests
RF: make fix0=True default for axis routines

I believe fix0 is benign and there are many TR=0 images out there; make
fix0=True the default so people don't often have to futz with the affine
in TR=0 case.
BF: strange error when passing bool as mask type

np.bool_ as very reasonable mask input type caused an error for
np.nan_to_num.  Only run nan_to_num if floating point mask type.
TST: Add tests for nipy_* scripts

We weren't testing the scripts until now.
BF: fix misspelled import of nibabel

The script appears to have been broken for a long time...  Tests are
good.
RF: refactor scripts to extend arguments and help

Add more help and command line arguments. Make tsdiffana work better
without a screen.
NF: setup helper for windows executable scripts

Now we have tests for the scripts, I finally find out that the scripts
weren't executable on Windows using the default install.

Add a distutils hack adapted from Twisted / IPython to make the
installed scripts executable from the Windows command line.
RF: run local script files through Python

On Windows, we can't run the local files through the shell because they
don't have needed ``.bat`` or ``.py`` extension. On Posix, we might have
the wrong Python interpreter named on the first line - for example -
"#!/usr/bin/env python" won't necessarily work for every platform, and
might not be the Python we're interested in.  So, run the scripts
through the interpreter we're running in already, if the scripts are
from the source.
BF: deal with spaces in paths for script arguments

Windows temporary directory names revealed the problem.
BF: check for symlinks looking for local scripts

Common case where we might not have installed the scripts is where we've
symlinked the code directory into the path somewhere; check for that
case.
BUG: viz: black background in PDF and SVG output
Remove trailing print
DOC: correct docstring
ENH: make it easier to use axes in slicers
DOC+TST: add examples to pca docstrings

Add doctests and some commentary to ``pca_image`` and ``pca``.
NF: added a module to handle mixed-effects
ENH: added the corresponding tests
ENH: Added an example illustrating the impact of mixed-effects model
BF: Changed the mixed-effects doctest for Travis
BF: Changed the mixed-effects doctest for Travis -- again