Move debiki-dao-pgsql Git repo to ../debiki-dao-rdb.git
Move debiki-dao-pgsql Git repo to ../debiki-dao-rdb.git

I'll probably rename the submodule from debiki-dao-pgsql to debiki-dao-rdb as
well?  Because it'd be reasonable to have it support both PostgreSQL and MySQL?

debiki/debiki-server-old,debiki/debiki-server-old,debiki/debiki-server-old,debiki/debiki-server-old