[COMMITTERS] pgsql: Improve low-level backup documentation.

Improve low-level backup documentation.

Our documentation hasn't really caught up with the fact that
non-exclusive backups can now be taken using pg_start_backup and
pg_stop_backup even on standbys.  Update.

David Steele, reviewed by Robert Haas and Michael Paquier

Discussion: http://postgr.es/m/f349b834-1443-ebf0-3c2a-965f944004d7@pgmasters.net

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9b1d48506a87a0ac61a1501a4253b6e6e524b87a

Modified Files
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doc/src/sgml/backup.sgml | 27 +++++++++++++++++++++------
doc/src/sgml/func.sgml   | 15 +++++++++++++--
2 files changed, 34 insertions(+), 8 deletions(-)