hdf5_der

[svn-r17027] Purpose: fix bug 1593

Description:
When using H5T_copy on committed datatypes that are already open, H5T_copy would
properly use the already existing shared struct, but would still deep copy all
of the fields in that struct.  This would cause memory leaks, and in the case of
a compound containing a vlen (or reference), the change in size would cause the
size of the resulting type to be set to an incorrect value.  Changed H5T_copy to
properly avoid deep copies when using a reopened shared struct.

Tested: jam, linew, smirom (h5committest)