hdf5: Use a stable URL

Only the current release is found in current/, but both the current
and older releases are found in releases/. Use the latter.

Closes #483
hdf5 1.8.12
Add :autoconf deps where missing
netcdf 4.3.0, fix build with clang

Closes #422.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>