Redirect XRC namespace URI to its schema.

Redirect requests to http://www.wxwidgets.org/wxxrc to xrc_schema.rnc file on
the trunk. This is a common practice, it helps with discovering the schema and
makes referencing it from elsewhere simpler than using the svn.wxwidgets.org
URI.


git-svn-id: https://svn.wxwidgets.org/svn/wxWebSite/trunk@1592 182c89d0-404e-469d-ac31-57daf6175630