pgsql: vacuumdb: enable parallel mode

vacuumdb: enable parallel mode

This mode allows vacuumdb to open several server connections to vacuum
or analyze several tables simultaneously.

Author: Dilip Kumar.  Some reworking by Álvaro Herrera
Reviewed by: Jeff Janes, Amit Kapila, Magnus Hagander, Andres Freund

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/a17923204736d8842eade3517d6a8ee81290fca4

Modified Files
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doc/src/sgml/ref/vacuumdb.sgml |   24 ++
src/bin/pg_dump/parallel.c     |    2 +-
src/bin/scripts/common.c       |   23 +-
src/bin/scripts/common.h       |    6 +
src/bin/scripts/vacuumdb.c     |  797 ++++++++++++++++++++++++++++++++--------
5 files changed, 691 insertions(+), 161 deletions(-)