Log Message:
hdf5 and hdf5-c++: fix up the threads option

Explicitly disable the hl interface of hdf5 with threads, removing
files from PLIST, and also preventing support for the C++ interface.

That is also why we won't enable threads by default anytime soon.
It is a specific option needed for some users. The jury is still out
if the threadsafe option or the C++ API has less users.

Not incrementing PKGREVISION, as build of hdf5-c++ with threads option
was broken anyway, as was PLIST of hdf5. Default builds without threads
are unaffected.