hdf5_der

[svn-r23725] Added two new features:
1. "-f filename" can create the test file somewhere other than
the current directory or <progname>.h5.  This allows running tests in different
filesystems, for example.
2. "-l w|r" can launch only the writer or the reader (default does both).
This allows launching writer (includes the "create file") in one process and
launching the reader somewhere else. (The "-f" helps too.)

Tested: h5committested.