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(-)