pgsql: Temporarily revert stats collector latch changes so we can ship

Temporarily revert stats collector latch changes so we can ship beta1.

This patch reverts commit 49340037ee3ab46cb24144a86705e35f272c24d5 and some
follow-on tweaking in pgstat.c. While the basic scheme of latch-ifying the
stats collector seems sound enough, it's failing on most Windows buildfarm
members for unknown reasons, and there's no time left to debug that before
9.2beta1. Better to ship a beta version without this improvement. I hope
to re-revert this once beta1 is out, though.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/cb2f2873d6b81ad7f0a9733ba738bfac0746fb7b

Modified Files
--------------
src/backend/postmaster/pgstat.c | 185 ++++++++++++++++++++++++--------------
1 files changed, 117 insertions(+), 68 deletions(-)