Move man page generation out into a separate script that's just invoked
from regen.sh, so that someone can run that separate script later if they
wish. Make that script more robust against problems such as empty podN
directories. Diagnose a missing pod2man and warn about old versions of
Pod::Man.
Also, remove the old programs used to do the initial conversion from HTML.
Enough post-conversion editing was done that they're no longer necessary
except for historical curiosity, and for that purpose they can be pulled
out of CVS.
(cherry picked from commit 0b21e24d0a96401033d55d3c079c954138b7c50e)
