hdf5_ep

[svn-r9949] Purpose:
Bug fix

Description:
h5diff sometimes will 'exit(status)' but if it is in parallel mode,
it needs to close up the workers and the MPI environment before exit(..).

Solution:
Created h5diff_exit() that will just exit in serial mode but does all
the shutdown properly if in parallel mode.

Platforms tested:
tested in heping, serial and parallel.

Misc. update: