Fix for bug #7540 (https://gna.org/bugs/index.php?7540).
This bug was reported by Alex Hansen (viochemist at gmail dot com). The problem was that the
function 'self.relax.generic.pdb.load()' had been renamed to 'self.relax.generic.pdb.read()'. The
correct function is now being called and the heteronucleus and proton name arguments, as well as the
'calc_vectors' argument have been removed.
