Suggested internationalization schema

Ass discusssed in last week's call, this is the suggested approach to
allowing for the use of the xml:lang attribute.  The LocalizedMessage type
can then be used for all human-readable mesaages.

<schema xmlns:xml="http://www.w3.org/XML/1998/namespace" ...>

    <import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/03/xml.xsd"/>

    <complexType name="LocalizedMessage">
        <simpleContent>
            <extension base="string">
                <attribute ref="xml:lang" use="optional"/>
            </extension>
        </simpleContent>
    </complexType>
...