RF - change tests to use get_data not asarray

Preparing to deprecate Image.__setitem__; the resample tests use direct
assignment into the array data.  Replace with img.get_data() calls.  The
tests also use asarray(img) which is deprecated; replace with get_data.

Small whitespace changes to resample.py
RF - deprecate Image.__setitem__

It is no longer used in the code as of the previous commit
NF - add iter_axis to default nipy.core.api
BF+RF - refactor image and fmri list, fix doctests

Enforce axis for from_image.
Explain why you can't pass images into the default constructor (when
default image iteration is disabled).
Fix doctests now I understand what's going on.
RF - simplify iter_axis

The function itself can be the generator, rather than returning one.
RF - raise error for default image iteration

Images should not iterate by default because, by default, they iterate
over the first axis, which is often not what we want.  For example, the
fourth axis may well be the time axis.  To avoid confusion and make this
explicit, we raise an error, preferring the explicit ``iter_axis``
function instead.
FIX: fixed the seed in test_gmm, and improved the syntax of the tests
FIX: fixed a bug in design matrix testing
STYLE: improved test style
Merge pull request #85 from bthirion/test-fixes

Test fixes for random errors
Merge pull request #80 from matthew-brett/rft-test-refactor

RF - reformat RFT tests, removed duplicates
Merge pull request #79 from matthew-brett/intrinsic-volumes-fixes

BF+TST - fix for wrapping in intrinsic volumes
RF - dummy object for testing is not a TestCase

The dummy object for testing the array-like interface of image was a
TestCase, but it is not designed to be a test case.
RF - use relative imports, test functions

Refactoring of tests to use relative imports, ready for move to
algorithms.statistics.
Removal of TestCase test classes in favor of test functions.
Merge pull request #86 from matthew-brett/stats-tests-refactor

RF - use relative imports, test functions
RF+BF - fix confusion of glm module and class

We were importing the 'glm.Model' class as 'glm', so the class looked
like the module, leading to confusing test failures
BF - adapt doctests to new formula framework
RF - use nipy tester instead of numpy version

Move __init__s to use relative imports
BF+TST - fixes to stats.models doctests

Update doctests for change to Formula and friends
Adding some tests for Yule-Walker function
Use new FP_6DP doctest option for many digit output
Edits and expansion of docstrings
DOC - expand and reformat model.py docstrings