Replace FFT filter by Butterworth filter

And replace default value for low and high frequency un signal.clean
by None instead of False.
Put warning into butterworth filter if values are wrong.
ENH: Minor fixed. Butterworth takes nD data.
Merge pull request #38 from AlexandreAbraham/butterworth_filter

Replace FFT filter by Butterworth filter
Small typo in plot_simulated_data.py
BUG: compute_epi_mask recomputed if n_jobs changed
BUG: Fix last commit bug
.tar.gz was not extracted
Fix dataset fetch by closing a temporary file prior to moving.
Merge pull request #40 from jmargeta/dataset_fetch_fix

Fix dataset fetch by closing a temporary file prior to moving.
Added icbm152_2009 dataset.
Corrected a typo in plot_rest_clustering.py
Small fixes in tutorial page (documentation)
Documentation fixes

Mainly langages corrections and typos.
Added hyperlinks to articles on bibliographic references.
Fixes in test

- Workaround for a Python 2.6/2.7 bug, that was triggered by check_niimgs()
- Make tests/test_signals.py work with numpy 1.3.0.
Fix test.
Add option to create directory in _get_dataset_dir
Corrected a typo in a doctype.
haxby_simple works with numpy 1.3 and sklearn 0.12

Added a workaround for missing features in either sklearn or numpy.
Added some user messages to the gen_rst extension

A few messages were added in the gen_rst extension for Sphinx.
Corrected some typos as well.