pgsql: Fix up the PQconnectionUsedPassword mess: create a separate

Log Message:
-----------
Fix up the PQconnectionUsedPassword mess: create a separate
PQconnectionNeedsPassword function that tells the right thing for whether to
prompt for a password, and improve PQconnectionUsedPassword so that it checks
whether the password used by the connection was actually supplied as a
connection argument, instead of coming from environment or a password file.
Per bug report from Mark Cave-Ayland and subsequent discussion.

Modified Files:
--------------
pgsql/doc/src/sgml:
libpq.sgml (r1.247 -> r1.248)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.247&r2=1.248)
release.sgml (r1.563 -> r1.564)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release.sgml?r1=1.563&r2=1.564)
pgsql/src/bin/pg_ctl:
pg_ctl.c (r1.90 -> r1.91)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_ctl/pg_ctl.c?r1=1.90&r2=1.91)
pgsql/src/bin/pg_dump:
pg_backup_db.c (r1.76 -> r1.77)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_db.c?r1=1.76&r2=1.77)
pg_dumpall.c (r1.98 -> r1.99)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dumpall.c?r1=1.98&r2=1.99)
pgsql/src/bin/psql:
command.c (r1.183 -> r1.184)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c?r1=1.183&r2=1.184)
startup.c (r1.141 -> r1.142)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/startup.c?r1=1.141&r2=1.142)
pgsql/src/bin/scripts:
common.c (r1.29 -> r1.30)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/common.c?r1=1.29&r2=1.30)
pgsql/src/interfaces/libpq:
exports.txt (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/exports.txt?r1=1.17&r2=1.18)
fe-auth.c (r1.134 -> r1.135)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c?r1=1.134&r2=1.135)
fe-connect.c (r1.353 -> r1.354)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c?r1=1.353&r2=1.354)
libpq-fe.h (r1.139 -> r1.140)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-fe.h?r1=1.139&r2=1.140)
libpq-int.h (r1.127 -> r1.128)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h?r1=1.127&r2=1.128)