hdf5_ep

[svn-r21611] Port r21610 to 1.8 branch

Purpose: Fix bug 7776

Description:
When H5Ocopy failed due to attempting to expand an invalid reference in an
attribute (or at any point after the destination object header was inserted
into the cache), it failed to clean up correctly.  Modified
H5O_copy_header_real to keep track of whether the object header was inserted
and take appropriate action on failure.

Tested: fedora (too minor for full commit test)