- Added a ZConfig directive 'large-file-threshold' to control
        the request content-size threshold at which a temporary file
        gets created. Use the same value for deciding between reading
        the whole request in memory or just a chunk inside
        webdav.NullResource.PUT().

      - Stitch newly-created object into it's container *before*
        calling it's PUT() method. This fixes an issue with
        OFS.File/OFS.Image that would result into reading the whole
        file in memory and wrapping it into a *single* Pdata object.

      - Import ZServer.CONNECTION_LIMIT variable *inside* the method
        that uses it. Before this, the variable was imported at the
        module level, thus binding it too early which would cause the
        ZConfig handler to have no real effect.