relax SVN archive

The index i was being overwritten in another place as well.

Fix for the creation of the het_atom data structure.

The index i was being overwritten!

Fixed the creation of the FORMUL record.

Fix for the creation of the HETNAM record. The None description value is replaced by 'Unknown'.

Modified the __get_chemical_name() to handle unidentifiable residue names.

Missing chain_ids are now caught and replaced by empty strings.

HETATM records with no residue info are now skipped in the HET record construction.

Fix for the main write_pdb() method.

Now the file object is sent into the specific write_pdb() method rather than the file path string.

Modified how non-standard residue information is collected and stored for future writing.

Fixes for the write_pdb() method for handling multiple structures better.