pgsql: Add new psql command \password for changing role password with

Log Message:
-----------
Add new psql command \password for changing role password with client-side
password encryption. Also alter createuser command to the same effect.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
alter_role.sgml (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/alter_role.sgml.diff?r1=1.2&r2=1.3)
create_role.sgml (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_role.sgml.diff?r1=1.4&r2=1.5)
psql-ref.sgml (r1.155 -> r1.156)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/psql-ref.sgml.diff?r1=1.155&r2=1.156)
pgsql/src/bin/psql:
Makefile (r1.55 -> r1.56)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/Makefile.diff?r1=1.55&r2=1.56)
command.c (r1.155 -> r1.156)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c.diff?r1=1.155&r2=1.156)
command.h (r1.22 -> r1.23)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.h.diff?r1=1.22&r2=1.23)
mainloop.c (r1.68 -> r1.69)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/mainloop.c.diff?r1=1.68&r2=1.69)
startup.c (r1.128 -> r1.129)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/startup.c.diff?r1=1.128&r2=1.129)
tab-complete.c (r1.142 -> r1.143)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/tab-complete.c.diff?r1=1.142&r2=1.143)
pgsql/src/bin/scripts:
createuser.c (r1.23 -> r1.24)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/createuser.c.diff?r1=1.23&r2=1.24)