Negative fluxes should be treated at normal fluxes
In principle we should be able to treat negative fluxes as any other flux. Sawicki+12 points this out in footnote 2. A good option would be to treat such fluxes normally if the user does not request them to be treated as upper limits. This should not incur any change in the pcigale.ini file format.
Request by Samir Salim.