Add a --locale switch to createdb, to ease the creation of databases with

Add a --locale switch to createdb, to ease the creation of databases with
different locales.  This is just syntactical sweetener over --lc-collate and
--lc-ctype.  Per discussion.

While at it, properly document --lc-ctype and --lc-collate in SGML docs,
which apparently were forgotten (or purposefully ommited?) when they were
created.