Added a new test to verify the MPIO can support independent
overlapping writes.
testphdf5.c:
Bracketed the MPIO write test with a #ifdef so that it is
tested only when the explicitely turned on.
Platform tested:
O2K.
big testphdf5.c file. Broke it into modules of related routines.
testphdf5.c -- main routine and global variables initialization plus
some ulitility routines.
t_file.c -- tests of file operations using parallel I/O.
t_dset.c -- tests of datasets operations.