NevowServer : added addInfoString to allow extensions to declare some read-only strings to be displayed in settings. Also renamed addExtension in addSettings for clarity.
<xsd:element name="Xenomai">
<xsd:complexType>
%(toolchain_gcc)s
<xsd:attribute name="XenoConfig" type="xsd:string" use="optional" default="xeno-config"/>
</xsd:complexType>
</xsd:element>