Set Bound Compton scattering option `on` to mean `norej`

[mainegra]

The bound Compton scattering option on uses a rejection technique which is slightly less efficient than norej. Although norej is the default, unsuspecting users might expect on to be the logical default choice. Perhaps a more logical approach would be to have on be what norej is and add a rej option in case one is interested for whatever reason to use the rejection technique.