.gitignore files, take two

Back here I asked what we were going to do about .gitignore files:
http://archives.postgresql.org/pgsql-hackers/2010-08/msg01232.php
The thread died off when the first git conversion attempt crashed and
burned; but not before it became apparent that we didn't have much
consensus. It seemed that there was lack of agreement as to:

1. Whether to keep the per-subdirectory ignore files (which CVS
insisted on, but git doesn't) or centralize in a single ignore file.

2. Whether to have the ignore files ignore common cruft such as
editor backup files, or only "expected" build product files.

It was pointed out that exclusion rules could be configured locally
to one's own repository, so one possible answer to issue #2 is to
have only a minimal ignore-set embodied in .gitignore files, and let
people who prefer to ignore more stuff set that up in local preferences.

Although this point wasn't really brought up during that thread, it's
also the case that the existing implementation is far from consistent
about ignoring build products. We really only have .cvsignore entries
for files that are not in CVS but are meant to be present in
distribution tarballs. CVS will, of its own accord, ignore certain
build products such as .o files; but it doesn't ignore executables for
instance. So unless you do a "make distclean" before "cvs update",
you will get notices about non-ignored files. That never bothered me
particularly but I believe it annoys some other folks. So really there
is a third area of disagreement:

3. What are the ignore filesets *for*, in particular should they list
just the derived files expected in a distribution tarball, or all the
files in the set of build products in a normal build?

We need to get some consensus on this now. Comments?

regards, tom lane