pgsql: Include more status information in walsender results

Include more status information in walsender results

Add the current xlog insert location to the response of
IDENTIFY_SYSTEM, and adds result sets containing start
and stop location of backups to BASE_BACKUP responses.

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=76129e7f14b4605db0a046e13abef0e255ffe007

Modified Files
--------------
doc/src/sgml/protocol.sgml            |   44 +++++++++++++++++----
src/backend/replication/basebackup.c  |   39 ++++++++++++++++++
src/backend/replication/walsender.c   |   27 +++++++++++--
src/bin/pg_basebackup/pg_basebackup.c |   70 ++++++++++++++++++++++++++++++++-
4 files changed, 167 insertions(+), 13 deletions(-)