Couple of minor buildfarm issues

One pretty silly point: I notice that
http://www.pgbuildfarm.org/index.html
says "The build farm software does not currently run on Windows".
This is out of date no?

One not so trivial question: do we have a policy about system/compiler
updates on buildfarm members? Arguably, if I'm running say OS X 10.2
and I update to 10.4, it's no longer the same machine and we should
retire the buildfarm ID (the "animal") and issue a new one to denote
that the results aren't necessarily comparable. (I choose the OS X
update as an example with malice aforethought, since in fact our older
branches do not work on 10.4.) Ditto for, say, a major gcc update.

At the very least it seems we need some longitudinal tracking of OS and
compiler and other software versions (eg Python version is relevant to
plpython). As best I can see from here, the identification of a
buildfarm member's software versions is static, and that isn't very
realistic unless we enforce it to be so.

regards, tom lane