pgsql: Get rid of client-code dependencies on the exact text of the

Log Message:
-----------
Get rid of client-code dependencies on the exact text of the no-password
error message, by using PQconnectionUsedPassword() instead. Someday
we might be able to localize that error message, but not until this
coding technique has disappeared everywhere.

Modified Files:
--------------
pgsql/src/bin/pg_ctl:
pg_ctl.c (r1.81 -> r1.82)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_ctl/pg_ctl.c.diff?r1=1.81&r2=1.82)
pgsql/src/bin/pg_dump:
pg_backup_db.c (r1.75 -> r1.76)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_db.c.diff?r1=1.75&r2=1.76)
pg_dumpall.c (r1.91 -> r1.92)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dumpall.c.diff?r1=1.91&r2=1.92)
pgsql/src/bin/psql:
command.c (r1.179 -> r1.180)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c.diff?r1=1.179&r2=1.180)
startup.c (r1.140 -> r1.141)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/startup.c.diff?r1=1.140&r2=1.141)
pgsql/src/bin/scripts:
common.c (r1.26 -> r1.27)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/common.c.diff?r1=1.26&r2=1.27)