pgsql: vacuumdb: don't prompt for passwords over and over

vacuumdb: don't prompt for passwords over and over

Having the script prompt for passwords over and over was a preexisting
problem when it processed multiple databases or when it processed
multiple analyze stages, but the parallel mode introduced in commit
a179232047 made it worse.

Fix the annoyance by keeping a copy of the password used by the first
connection that requires one.  Since users can (currently) only have a
single password, there's no need for more complex arrangements (such as
remembering one password per database).

Per bug #13741 reported by Eric Brown.  Patch authored and
cross-reviewed by Haribabu Kommi and Michael Paquier, slightly tweaked
by Álvaro Herrera.

Discussion: http://www.postgresql.org/message-id/20151027193919.931.54948@wrigleys.postgresql.org
Backpatch to 9.5, where parallel vacuumdb was introduced.

Branch
------
REL9_5_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/5094da99b901df42580b6e7494d036ee4be9eb81

Modified Files
--------------
src/bin/scripts/clusterdb.c  |    2 +-
src/bin/scripts/common.c     |   39 +++++++++++++++----------
src/bin/scripts/common.h     |    4 +--
src/bin/scripts/createlang.c |    8 ++---
src/bin/scripts/createuser.c |    4 +--
src/bin/scripts/droplang.c   |    8 ++---
src/bin/scripts/dropuser.c   |    4 +--
src/bin/scripts/reindexdb.c  |    8 ++---
src/bin/scripts/vacuumdb.c   |   66 +++++++++++++++++++++++++++++++++++-------
9 files changed, 98 insertions(+), 45 deletions(-)