Improve formatting of create_help.pl and plperl_opmask.pl output.

Improve formatting of create_help.pl and plperl_opmask.pl output.

Adjust the whitespace in the emitted files so that it matches
what pgindent would do.  This makes the generated files look
like they match project style, and avoids confusion if someone
does run pgindent on the generated files.

Also, add probes.h to pgindent's exclusion list, because it can
confuse pgindent, plus there's not much point in processing it.

Daniel Gustafsson, additional fixes by me

Discussion: https://postgr.es/m/79ed5348-be7a-b647-dd40-742207186a22@2ndquadrant.com