ENH: fast reads on large gzip files

Fixes #209
BUG: fix previous commit

Acutally use the opening logic
NF: get_unscaled method for Analyze array proxy

Add get_unscaled for those of us who like to get the raw unscaled data
from the array.
TST: tests for read_img_data function

Test the behavior of the `read_img_data` function as of commit 6d8f6c6.
This is before the changes to Analyze image types to make the header
slope, intercept and data offset be consumed during write, and reset to
default values.  These tests pass against that commit but fail against
current master, which is 62f4c70.
RF: replicate read_img_data behavior + deprecate

Do approximate replication of the old behavior of read_img_data.

Deprecate with suggestions about alternatives.
fix endian value in gifti
fix b64encoding for no newline in outputs
fixes + backcompat test
NF: add setuptools-aware package checking

Add extra dictionary arg to package_check so that package_check knows
its working with setuptools, and can fill the dependencies in the
dictionary accordingly.
RF: adapt setup.py dependency checks to setuptools.

This is still a disaster if running normal ``python setup_egg.py
install`` - but no more of a disaster than before.
TST+BF: extend comments and tests on bad gii file

Luckily one of our test files uses a couple of bad encoding values, and
carriage returns in base64 data.  Comment on this and add explicit
checks of endianness.
TST: check gifti bad contents gets written as good

Check for presence of bad tags and their removal by loading and saving
the file.
BF+RF: refactor base64 and array to text for py3

Refactor base64 imports to use the standard interface.

Replace use of np.savetxt and BytesIO with a small custom function for
writing comma-delimited text.  Fixes Python 3 incompatibility mixing
output from BytesIO with strings.
RF: remove duplicate test

We're testing backwards compatibility in `test_base64_written`
TST: add round trip tests for example images

Add tests for saved / loaded example images.
Merge pull request #234 from nipy/package_check-fix

MRG: adapt package_check to setuptools

Now pip is working pretty well, adapt package_check to fill setuptools
arguments instead of giving errors, when setuptools has been imported.
Merge pull request #224 from matthew-brett/reworking-raw-scaling

MRG: fix and deprecate read_img_data function

The read_img_data function was a hack to help Michael get the raw image
data out of Nifti images without applying the image scaling. The new
API for consumable values in the header broke this code, but it was a
bad idea in the first place and it was in any case broken for MINC.

Add a 'get_unscaled' method for the ArrayProxy object to give a cleaner
API to get the unscaled data. Try and replicate the old behavior of
read_img_data but deprecate so we don't need to maintain it long term.
Merge pull request #235 from matthew-brett/caret-fixes-continued

MRG: fixes to gifti writing

Closes https://github.com/nipy/nibabel/issues/230

Use standard b64 encoding instead of legacy, and fix written endian code (we were using the wrong code).   Extend tests to make sure we can read files we wrote before this fix.
BF: fix test failures on PPC buildbot

Test failure from older Numpy lacking order keyword to ravel method.

Test failure expecting LittleEndian from written file, when BigEndian is
correct
BF: fix for failed file deletion in Windows

Windows refuses to delete a file still open in a Python object.