legal-info: split _LICENSE and _REDISTRIBUTE constants

Currently packages can be described in two ways: proprietary (tarball not
saved, license not described in further detail), and others (tarball
saved, license described).

Split the logic to allow the license to be always described whether or not
the source code can be redistributed.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>