Yet another HDF5 waf fix.

This seems to work on my Ubuntu 14.04 VM.  It works on my Mac.  It's possibly broken on a Cray supercomputer, but I don't understand how h5cc can possibly work on that system.

git-svn-id: svn+ssh://svn.code.sf.net/p/xmds/code/trunk/xpdeint@2966 41b19578-b77a-4e3b-9682-c8570d237623