hdf5_der

[svn-r26038] Various improvements to parallel multi dataset test:
- Prints the seed value on error
- Continues on error
- All ranks return error if any rank fails
- Closes/reopens file after a write to ensure consistency
- Changed to use full independent path when using independent I/O.  Note that
  some versions of MPICH seem to have trouble with the previous implementation
  (collective path/independent low level I/O) so it may be worth investigating
  this when the next version of MPICH comes out
Added multi dataset tests to cmake files
Fixed comment in H5Dio.c

Tested: jam