This fixes a few typos and small mistakes; it also cleans a few
minor stylistic issues.  The biggest functional change is that
Gen_fmgrtab.pl no longer knows the OID of language 'internal'.

Author: John Naylor
Discussion: https://postgr.es/m/CAJVSVGXAkwbk-A9QHHHf00N905kKisyQbaYwKqaRpze_gPXGfg@mail.gmail.com