prefixed-outputs. Bet wrapper uses new outprefix option.

used as a wildcard - all files which begin with outprefix can be specified
as keyword arguments and LOADed.

in file.

stdout/stderr streams go.

gives $FSLDEVDIR precedence, and also allows a global override.

stdout/stderr, and also redirects it to real stdout/stderr.

get image data as numpy array.

AtlasDescription.labels list.

    - not all atlases have a 2mm version
    - label atlas value does not correspond to its index in the
      AtlasDescription.labels list.

fixed a small documentation error as well
added a warning about missing if __name__ == '__main__' guard in script