Fixed CHICAGO: Bug 2121 - h5diff - incorrect and lack of output for the
different set of attributes (different number and names)
Description:
Merged from HDF5 trunk r20294
Previously h5diff compared attributes correctly only when two objects have
the same number of attributes and attribute names are identical.
Also didn't display useful information about attribute difference.
This fix covers all other cases.
This fixes both issues.
Tested:
jam (linux32-LE), amani (linux64-LE), heiwa (linuxppc64-BE)
