cvs chapters in our docs

Attached is a patch which adds a chapter to git in our documentation,
around where we have several chapters about cvs today. It also removes
a few very out of date comments about cvs (really, nobody has a 28k8
modem and does cvs over it today. Even your cellphone is orders of
magnitude faster than that).

Other than this patch, I would suggest that we completely remove the
following two chapters:

http://www.postgresql.org/docs/8.4/static/cvs-tree.html -- because
anybody doing anything with branching or tagging today is *not* going
to be using cvs, they will be using git. Let's not lead people down
the wrong path :-)

http://www.postgresql.org/docs/8.4/static/cvsup.html -- does anybody
ever use this? It's a complete PITA to get cvsup working on any
platform I know of. And since we already allow both rsync and git to
get the full repository, there's not much point to it.

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/