I hate this function :)

First it starts with this very encouraging comment:
      /* FIXME: This is disgustingly slow */

Indeed, it iterates over *all* the individuals we know about and then check if each of those has a persona associated with it.

So this is slow but also wrong if the individual manager isn't prepared. Typically, empathy-chat shouldn't have to know about all the individuals around so doesn't have any reason to keep an individual manager around during all its lifetime. So this function creates a new individual manager, doesn't find any individual and then destroy it right away!

Why not just craft a new TpfPersona from the TpContact as we already do in 
empathy_create_individual_from_tp_contact()?