pkgsrc notion that free software should not depend on non-free
software (because that results in not having distributable binary
packages, and makes the build fail) unless skipping the dependency
renders the software non-useful.
(The hdf web page says that the default binary builds of hdf include
szip support, but then go on about how users that don't qualify for
the no-cost license have to install a different version.)
If someone who grasps hdf5 can say that hdf5 w/o szip is generally not
useful, we can turn this back on and disable by default the hdf5
option in octave.
(yes I know there is the 1.8 branch, but I don't want to experiment
right now)
changes: many fixes, some C++ API improvements
pkgsrc change: DESTDIR support
since they always need a C compiler, even when the source code is
completely in C++.
For some other packages, stated in the comment that a C compiler is
really not needed.