pgsql-server: Add docs for initdb --auth.

Log Message:
-----------
Add docs for initdb --auth.

Modified Files:
--------------
    pgsql-server:
        configure (r1.379 -> r1.380)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/configure.diff?r1=1.379&r2=1.380)
        configure.in (r1.369 -> r1.370)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/configure.in.diff?r1=1.369&r2=1.370)
    pgsql-server/doc/src/sgml/ref:
        initdb.sgml (r1.31 -> r1.32)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/ref/initdb.sgml.diff?r1=1.31&r2=1.32)
    pgsql-server/src:
        Makefile.global.in (r1.190 -> r1.191)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/Makefile.global.in.diff?r1=1.190&r2=1.191)
    pgsql-server/src/backend/commands:
        dbcommands.c (r1.137 -> r1.138)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/dbcommands.c.diff?r1=1.137&r2=1.138)
    pgsql-server/src/bin/initdb:
        Makefile (r1.41 -> r1.42)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/initdb/Makefile.diff?r1=1.41&r2=1.42)
        initdb.c (r1.45 -> r1.46)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/initdb/initdb.c.diff?r1=1.45&r2=1.46)
    pgsql-server/src/include:
        port.h (r1.45 -> r1.46)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/port.h.diff?r1=1.45&r2=1.46)
    pgsql-server/src/port:
        dirmod.c (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/port/dirmod.c.diff?r1=1.12&r2=1.13)