Checks to see if the PDB file has been deprecated and, if so, what the new ID is.

def parse_deprecation(self):
        '''Checks to see if the PDB file has been deprecated and, if so, what the new ID is.'''
        deprecation_tag = self.main_tag.getElementsByTagName("PDBx:pdbx_database_PDB_obs_sprCategory")
        assert(len(deprecation_tag) <= 1)
        if deprecation_tag:
            deprecation_tag = deprecation_tag[0]

            deprecation_subtag = deprecation_tag.getElementsByTagName("PDBx:pdbx_database_PDB_obs_spr")
            assert(len(deprecation_subtag) == 1)
            deprecation_subtag = deprecation_subtag[0]
            assert(deprecation_subtag.hasAttribute('replace_pdb_id'))
            assert(deprecation_subtag.hasAttribute('pdb_id'))
            old_pdb_id = deprecation_subtag.getAttribute('replace_pdb_id').upper()
            new_pdb_id = deprecation_subtag.getAttribute('pdb_id').upper()

            if self.pdb_id == old_pdb_id:
                self.deprecated = True
                self.replacement_pdb_id = new_pdb_id
            else:
                assert(self.pdb_id == new_pdb_id)