message: Syntax fix and more examples in Looks.mtlx
  * Remove unneeded XInclude from MaterialBasic.mtlx
  * Syntax fix and additional examples in Looks.mtlx
  "propertysetname" attribute should be "propertyset", added examples of variantset/variants/variantassigns.
diff: </shaderref>
  </material>
  + <variantset name="varset">
  + <variant name="dry">
  + <parameter name="wetgain" type="float" value="0.0"/>
  + </variant>
  + <variant name="wet">
  + <parameter name="wetgain" type="float" value="1.0"/>
  + </variant>
  + <variant name="damp">
  + <parameter name="wetgain" type="float" value="0.2"/>
  + </variant>
  + </variantset>
  +
  <collection name="c_plastic" includegeom="/a/g1,/a/g2,/a/g5"/>
  <collection name="c_metal" includegeom="/a/g3,/a/g4"/>
  <collection name="c_lamphouse" includegeom="/a/lamp1/housing*Mesh"/>
  <materialassign name="ma3" material="mheadlight" geom="/a/b/headlight"/>
  <visibility name="v1" viewergeom="/a/b/headlight" vistype="shadow" geom="/" visible="false"/>
  <visibility name="v2" viewergeom="/a/b/headlight" vistype="shadow" collection="c_lamphouse"/>
  - <propertysetassign name="psa1" propertysetname="standard" geom="/"/>
  + <propertysetassign name="psa1" propertyset="standard" geom="/"/>
  </look>
  <look name="lookB">
  <materialassign name="ma4" material="Mplastic2" collection="c_plastic"/>
  <materialassign name="ma5" material="Mmetal2" collection="c_metal"/>
  - <propertysetassign name="psa2" propertysetname="standard" geom="/"/>
  + <propertyassign name="pa1" property="matte" type="boolean" value="true" geom="/g/holdout,/g/holdout2"/>
  + <propertysetassign name="psa2" propertyset="standard" geom="/"/>
  + <variantassign name="va1" variantset="varset" variant="damp"/>
  <!-- make the setgeom invisible to camera but still visible to shadows and reflections -->
  <visibility name="v3" vistype="camera" collection="c_setgeom" visible="false"/>
  </look>
  