pgsql: pg_dump et al: Add --if-exists option

pg_dump et al: Add --if-exists option

This option makes pg_dump, pg_dumpall and pg_restore inject an IF EXISTS
clause to each DROP command they emit. (In pg_dumpall, the clause is
not added to individual objects drops, but rather to the CREATE DATABASE
commands, as well as CREATE ROLE and CREATE TABLESPACE.)

This allows for a better user dump experience when using --clean in case
some objects do not already exist. Per bug #7873 by Dave Rolsky.

Author: Pavel Stěhule
Reviewed-by: Jeevan Chalke, Álvaro Herrera, Josh Kupershmidt

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9067310cc5dd590e36c2c3219dbf3961d7c9f8cb

Modified Files
--------------
doc/src/sgml/ref/pg_dump.sgml | 14 ++++++-
doc/src/sgml/ref/pg_dumpall.sgml | 11 +++++
doc/src/sgml/ref/pg_restore.sgml | 14 ++++++-
src/bin/pg_dump/pg_backup.h | 1 +
src/bin/pg_dump/pg_backup_archiver.c | 73 +++++++++++++++++++++++++++++++++-
src/bin/pg_dump/pg_dump.c | 7 ++++
src/bin/pg_dump/pg_dumpall.c | 22 ++++++++--
src/bin/pg_dump/pg_restore.c | 11 +++++
8 files changed, 146 insertions(+), 7 deletions(-)