pgsql: Force a checkpoint before committing a CREATE DATABASE command.

Log Message:
-----------
Force a checkpoint before committing a CREATE DATABASE command.  This
should fix the recent reports of "index is not a btree" failures,
as well as preventing a more obscure race condition involving changes
to a template database just after copying it with CREATE DATABASE.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        backup.sgml (r2.68 -> r2.69)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/backup.sgml.diff?r1=2.68&r2=2.69)
    pgsql/src/backend/commands:
        dbcommands.c (r1.160 -> r1.161)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/dbcommands.c.diff?r1=1.160&r2=1.161)