Get rid of the need for manual maintenance of the initial contents of

pg_attribute, by having genbki.pl derive the information from the various
catalog header files.  This greatly simplifies modification of the
"bootstrapped" catalogs.

This patch finally kills genbki.sh and Gen_fmgrtab.sh; we now rely entirely on
Perl scripts for those build steps.  To avoid creating a Perl build dependency
where there was not one before, the output files generated by these scripts
are now treated as distprep targets, ie, they will be built and shipped in
tarballs.  But you will need a reasonably modern Perl (probably at least
5.6) if you want to build from a CVS pull.

The changes to the MSVC build process are untested, and may well break ---
we'll soon find out from the buildfarm.

John Naylor, based on ideas from Robert Haas and others