NF: add script_test attribute to script tests

We need to be able to skip the script tests to make the bdist-egg-tests
Makefile target work.
BF: update Makefile targets for testing

The testing commands were breaking because:

* doctests were failing from ``nibabel.test()`` because of numpy's
  defult behavior of stripping the namespace before running the doctest.
* The bdist-egg-tests target fails because we now have script tests, and
  these need the new bin directory on the path.  This is too annoying to
  implement, so just script the script tests.
RF: use PYTHON variable for python binary

Use variable to allow user to set the python binary used for tests etc.
NF: add makefile target for installing from sdist
RF: simplify and generalize run_mod_cmd

`run_mod_cmd` was getting complicated and it was failing on Windows.
Because it was complicated I couldn't work out why it was failing.
Simplify by writing the script in the temporary directory rather than
trying to use a long command string.  The refactoring may mean that
paths with spaces will work.
BF: use raw strings for Windows paths in script

Windows paths inside the script were not being properly escaped leading to
obscure errors - for example for a path that happened to contain an x after a
backslash.  Use raw strings for variables interpolated into the script.
Merge pull request #199 from matthew-brett/makefile-updates

MRG: updates to Makefile targets and testing

Automated testing from the Makefile was broken; fix and add new testing
Makefile target.
Merge pull request #202 from matthew-brett/safer-mod-command

RF: refactoring the nisext routines

Make the nisext tester routines simpler to make them easier to debug,
and to fix an error on windows. We should probably deprecate the
testers routines at some point because virtualenvs are a better
solution to this problem, and the buildbot does a fair amount of this
testing.
TST: add some tests for Ellipsis and fileslice

Confirm that appending None (newaxis) to an Ellipsis appends a new axis.
NF: add coverage / coveralls for travis build

Adapted from https://github.com/scipy/scipy/pull/2907
Merge pull request #204 from matthew-brett/add-coveralls

TST: add coverage / coveralls for travis build

Add automatic coverage report using coveralls

Adapted from scipy/scipy#2907
Add function to save FreeSurfer annotation files.
Add a test for FreeSurfer annotation file writing.
Add test coverage for reading FreeSurfer annot files with
orig_inds=True after they are written with write_annot.
Merge pull request #206 from ohinds/save_annot

Add function to save FreeSurfer annotation files.
DOC: whitespace clean for orientations