[Fons Adriaensen]
This makes is backwards compatible, as no new field is required
in the descriptor struct.
AFAICS, binary compatibility is not compromised by an expanded
descriptor struct, as long as additional members are appended to the
struct.
(That is not to say it's hugely preferable introducing a new char **
PortValueLabels to appending these to the existing PortNames array -
just to point out that it is possible without breaking things.)
Cheers, Tim