pgsql: Add archive_mode='always' option.

Add archive_mode='always' option.

In 'always' mode, the standby independently archives all files it receives
from the primary.

Original patch by Fujii Masao, docs and review by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ffd37740ee6fcd434416ec0c5461f7040e0a11de

Modified Files
--------------
doc/src/sgml/config.sgml                      |   13 +++++++--
doc/src/sgml/high-availability.sgml           |   39 +++++++++++++++++++++++++
src/backend/access/transam/xlog.c             |   22 ++++++++++++--
src/backend/access/transam/xlogarchive.c      |    5 +++-
src/backend/postmaster/postmaster.c           |   37 +++++++++++++++++------
src/backend/replication/walreceiver.c         |   10 +++++--
src/backend/utils/misc/guc.c                  |   21 ++++++-------
src/backend/utils/misc/postgresql.conf.sample |    2 +-
src/include/access/xlog.h                     |   13 +++++++--
9 files changed, 133 insertions(+), 29 deletions(-)