added a closing operation to the masker to avoid 'gaps' in the mask
merged opening and closing into the single parameter opening
changed parameters in nifti-masker to only keep opening
changed parameters in nifti-masker to only keep opening & removed trailing tab-character on blank line
Merge branch 'master' of https://github.com/nilearn/nilearn into mask_closing
clarified docstring as per the request of G. Varoquaux
Merge pull request #145 from rphlypo/mask_closing

added a closing operation to the masker to avoid 'gaps' in the mask