Rewrite the log(x) factor in lognormal logp in the right place.
Rewrite the log(x) factor in lognormal logp in the right place.

The change is non-functional (we switched the signs), but the
log(x) and sum_log_x prefactors need to come for the next step
logZ and not the initial logZ.

probcomp/cgpm,probcomp/cgpm