We have the relations continuously locked, but not open, so relcache
pointers are not guaranteed to be stable.  Per buildfarm member
prion.

Ashutosh Bapat.  I fixed a typo.

Discussion: http://postgr.es/m/CAFjFpRcRBqoKLZSNmRsjKr81uEP=ennvqSQaXVCCBTXvJ2rW+Q@mail.gmail.com