Workaround for ndimage.affine_transform endianness bug

Need to swap the bytes of the output array when its endianness is not native.
Added test.
Add nilearn/data as a data dir

Otherwise the MNI template is missing when installing nilearn with setup.py
Change the default dataset download directory to ~/nilearn_data

* Tweak the tests to use absolute paths and put the temporary data in
  tmpdir so that it gets cleaned up during teardwon. Also remove PEP8
  warnings.
* Update doc mentionning nilearn_data
Merge pull request #281 from lesteve/default-nilearn-data-in-home

Change the default dataset download directory to ~/nilearn_data
Merge pull request #279 from lesteve/resample-img-non-native-endianness

Workaround for ndimage.affine_transform endianness bug
Merge pull request #280 from lesteve/add-data-to-setup-py

Add nilearn/data as a data dir in setup.py
Minor clean-up of the FWHM to sigma conversion

No need to use 'fwhm' on both sides of the = sign and the comment about
not using /= with numpy scalar wasn't entirely helping.
Merge pull request #283 from lesteve/fwhm-to-sigma-conversion-tweak

[MRG] Minor clean-up of the FWHM to sigma conversion
ENH: remove warnings with default settings

IMHO default settings should never raise warnings
[ENH] allow specification of vmin in plot_stat_map

This allows plotting e.g. p-values with a sensible use of the colorbar. Proposed after discussion with @mrahim and @lesteve
Revert "[ENH] allow specification of vmin in plot_stat_map"

This reverts commit 165591a64dad335581a9881844d23fd673c84a41.
Fix plot_haxby_anova_svm example
ENH: error capture for wrong session length

Should prevent bugs like in #284
Fix auto threshold in img_plotting.py

Replace + by - to ensure that some voxels pass the threshold
Merge pull request #285 from lesteve/auto-threshold

Fix auto threshold in img_plotting.py
Parallelization of CanICA
Merge pull request #276 from banilo/par_ica

Parallel() for CanICA class
PEP8 fixes
completed docstrings
corrected add_overlay() docstring