hdf5_ep

[svn-r14096] There're 3 changes in this checkin as below:
  1. In H5Dwrite and H5Dread, let the data buffer point to a fake address if the application passes
     in an empty buffer.  This is mainly for MPIO programs that some processes may not have any 
     data to write or read but still participate the I/O.  This solution solves some MPI's problem
     like the ChaMPIon on tungsten which doesn't support empty buffer.
  2. The ChaMPIon on tungsten doesn't support complex derived MPI data type correctly and collective
     I/O when some processes don't have any data to write or read correctly.  Detect the compiler
     "cmpicc" in the system-specific config file and set the variables for these two cases to false.
     The PHDF5 library already has set up a way to switch collective chunked I/O to independent 
     under these two cases.
  3. A bug fix - During the work of the optimization for compound data I/O, the case for switching
     collective chunked I/O to independent I/O was leftout.  Fixed it by adding I/O caching to it in
     H5D_multi_chunk_collective_io in H5Dmpio.c.

Tested on tungsten, cobalt, and kagiso for parallel; on linew and smirom for serial.