#234 read HETERO groups in mmCIF Assembly files (PDBe)

[Angel Herraez]

PDBe (EBI) has been providing "assembly files" with the (curated) most likely biological unit for every protein.
Since Proteopedia started to use these models instead of the RCSB PDB files, we are encountering several idiosyncrasies. Their assembly CIF format is different in several respects to the standard (mm)CIF format.
We have noticed that Jmol's popup menu, Select > Hetero > by HETATM has an empty list of het groups for every assembly mmCIF file.
I suppose this needs some fix in the reader. The relevant field with the list of HET group codes and long names seems to be _pdbx_entity_nonpoly.

Sample file: http://www.ebi.ac.uk/pdbe/static/entry/download/1hho-assembly-1.cif.gz
Hemoglobin tetramer, with PO4 , HEM , OXY , HOH