This probably doesn't save anything meaningful in terms of
performance, but making the code simpler is a good idea anyway.

Code by Beena Emerson, extracted from a larger patch by Jeevan
Ladhe, slightly adjusted by me.

Discussion: http://postgr.es/m/CAOgcT0ONgwajdtkoq+AuYkdTPY9cLWWLjxt_k4SXue3eieAr+g@mail.gmail.com