>Perhaps also have a bandpass=None option that would try to do a bolometric flux, integrating from 0 to infinity (or at least over the whole wavelength range that the SED is defined if it is a LookupTable).

This should now work too.  I decided not to have this as a default kwarg; you have to specify `None` explicitly.  I was slightly worried that, otherwise, a user might accidentally forget to specify a bandpass, galsim would interpret that as a bolometric flux request (and not raise an exception), and they would get difficult to trace weird results.