pgsql-server: Use standard macro for psql binary file open.

Log Message:
-----------
Use standard macro for psql binary file open. Add comment explaining
control-z requirement.

Modified Files:
--------------
pgsql-server/src/bin/psql:
command.c (r1.118 -> r1.119)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/psql/command.c.diff?r1=1.118&r2=1.119)
common.h (r1.36 -> r1.37)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/psql/common.h.diff?r1=1.36&r2=1.37)
copy.c (r1.48 -> r1.49)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/psql/copy.c.diff?r1=1.48&r2=1.49)
psqlscan.l (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/psql/psqlscan.l.diff?r1=1.4&r2=1.5)
pgsql-server/src/include:
c.h (r1.165 -> r1.166)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/c.h.diff?r1=1.165&r2=1.166)