RF+BK+OCTV: use shortcut logical "or" ("||") instead of element-wise "or" ("|"). Enhances Octave compatibility
RF+ENH: better detection of empty input
BF+DOC: allow NaN values for feature selection
WEB: explain concepts better (including chunks and targets). ACK:Thomas Hartmann.
BF: do not ignore cosmomvpa_concepts.rst
WEB: special note about importance of chunks and targets. ACK:Thomas Hartmann.
WEB: indicate that input can also be FT struct. ACK:Thomas Hartmann
DOC+SML: explain input can be struct