Sync Rep v19

Latest version of Sync Rep, which includes substantial internal changes
and simplifications from previous version. (25-30 changes).

Includes all outstanding technical comments, typos and docs. I will
continue to work on self review and test myself, though actively
encourage others to test and report issues.

Interesting changes

* docs updated

* names listed in synchronous_standby_names are now in priority order

* synchronous_standby_names = "*" matches all standby names

* pg_stat_replication now shows standby priority - this is an ordinal
number so "1" means 1st, "2" means 2nd etc, though 0 means "not a sync
standby".

The only *currently* outstanding point of discussion is the "when to
wait" debate, which we aren't moving quickly towards consensus on at
this stage. I see that as a "How should it work?" debate and something
we can chew over during Alpha/Beta, not as an immediate blocker to
commit.

Please comment on the patch and also watch changes to the repo
git://github.com/simon2ndQuadrant/postgres.git

--
Simon Riggs http://www.2ndQuadrant.com/books/
PostgreSQL Development, 24x7 Support, Training and Services