Merge pull request #3406 from CyrusBiotechnology/delucasl/write_seqres
From @decarboxy at Cyrus:
optionally output SEQRES lines in PDB files
This PR extends the pdb outputter to produce SEQRES records.
This feature is off by default and can be turned on with -out:file:write_seqres_records
also added a test that exercises the feature. No integration test changes expected.