SVGHMI: Makes error when HMI tree is not well formed. Prevents multiple and non-first HMI_NODE, and ensure that all paths in HMI tree are unique.
<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>