Make reformat_dat_file.pl preserve all blank lines.

Make reformat_dat_file.pl preserve all blank lines.

In its original form, reformat_dat_file.pl smashed consecutive blank
lines to a single blank line, which was helpful for mopping up excess
whitespace during the bootstrap data format conversion.  But going
forward, there seems little reason to do that; if developers want to
put in multiple blank lines, let 'em.  This makes it conform to the
documentation I (tgl) wrote, too.

In passing, clean up some sloppy markup choices in bki.sgml.

John Naylor

Discussion: https://postgr.es/m/28827.1523039259@sss.pgh.pa.us