pgsql: Avoid trying to open /dev/tty on Win32.

Log Message:
-----------
Avoid trying to open /dev/tty on Win32. Some Win32 systems have
/dev/tty, but it isn't a device file and doesn't work as expected.

This fixes a known bug where psql does not prompt for a password on some
Win32 systems.

Backpatch to 8.1.X.

Robert Kinberg

Tags:
----
REL8_1_STABLE

Modified Files:
--------------
pgsql/src/bin/psql:
command.c (r1.154.2.1 -> r1.154.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c.diff?r1=1.154.2.1&r2=1.154.2.2)
pgsql/src/port:
sprompt.c (r1.12 -> r1.12.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/sprompt.c.diff?r1=1.12&r2=1.12.2.1)