hdf5_ep

[svn-r2625] Purpose:
    Bug fix and feature
Description:
    It could not find a working h5dump to process the hdf5 files.
    This could be because h5dump is not installed in $PATH or
    a disfunctional one is found. (E.g. arabica:/usr/sdt/bin/h5dump
    does not work.)
    Setting it to ./h5dump or $PWD/h5dump does not work because
    when h5dump is used, it has "cd testfiles", a different place.
Solution:
    Set H5DUMP with the current absolute path (used `pwd` instead
    of $PWD which is sometimes not set for whatever reason.)
    Also add a feature to allow H5DUMP to be set to a different
    value by hand.  For example, if the h5dump just built is not
    working correctly, one can do "H5DUMP=/usr/local/bin/h5dump make check"
    to bypass the broken h5dump.
Platforms tested:
    arabica