hdf5_ep

[svn-r26189] Merge revision 26149 to 1.8 branch

Fix potential memory error reported by valgrind in
H5D__link_chunk_collective_io.  This would occur when performing collective I/O
on a dataset with only 1 chunk, and a participating process had nothing to read
or write.

Tested: jam, koala, ostrich (h5committest); in trunk and 1.8