Checks to make sure that each atom type is unique per residue.

def get_atom_serial_numbers_from_pdb_residue_ids(self, pdb_residue_ids, ignore_these_atoms = [], ignore_these_conformations = []):
        '''Checks to make sure that each atom type is unique per residue.'''
        atom_list = []
        for pdb_residue_id in pdb_residue_ids:
            chain = pdb_residue_id[0]
            residue_id = pdb_residue_id[1:]
            if chain in self.residues and residue_id in self.residues[chain]:
                residue = self.residues[chain][residue_id]
                for record_type, atoms in residue.records.iteritems():
                    freq = {}
                    for atom in atoms:
                        if atom.name not in ignore_these_atoms and atom.conformation not in ignore_these_conformations:
                            atom_list.append(atom.serial_number)
        return atom_list