default option set for math/octave depends on non-free software

[Taylor R Campbell <campbell%mumble.net@localhost>]

By default, math/octave has the option hdf5 enabled, which makes it
depend on devel/hdf5, which in turn has the option szip enabled, which
makes it depend on the non-free software archivers/szip.

I wish that nothing that is itself free software in pkgsrc would
depend on non-free software by default.  (I'd rather not see non-free
software in pkgsrc at all, but that's a separate issue.)  It seems
especially silly that for a GNU program such as GNU Octave, pkgsrc
would do that!