hdf5_ep

[svn-r23469] Description:
    Change h5diff_exit() routine to always return a zero exit code when running
in parallel, since returning a non-zero exit code can cause MPI implementations
to print output and that can throw off our "expected output" comparisons.

    Note that this change only changes the exit code for situations where an
incorrect command-line parameter was given - ph5diff was already returning a
zero exit code for all "normal" executions, including those where a serial
h5diff would return a non-zero exit code.

Tested on:
    Mac OSX/64 10.8.3 (amazon) w/parallel
    (Too minor to require h5committest)