This patch teaches genbki.pl to replace pg_language names by OIDs
in much the same way as it already does for pg_am names etc, and
converts pg_proc.dat to use such symbolic references in the prolang
column.

Aside from getting rid of a few more magic numbers in the initial
catalog data, this means that Gen_fmgrtab.pl no longer needs to read
pg_language.dat, since it doesn't have to know the OID of the "internal"
language; now it's just looking for the string "internal".

No need for a catversion bump, since the contents of postgres.bki
don't actually change at all.

John Naylor

Discussion: https://postgr.es/m/CAJVSVGWtUqxpfAaxS88vEGvi+jKzWZb2EStu5io-UPc4p9rSJg@mail.gmail.com