message: Fix output type of blackbody node
  This changelist fixes the output type of the blackbody node, aligning it with the specification.
diff: <input name="anisotropy" type="float" value="0.0" uimin="0.0" uimax="1.0" />
  <output name="out" type="vector2" />
  </nodedef>
  +
  + <!--
  + Node: <blackbody>
  + Returns the radiant emittance of a blackbody radiator with the given temperature.
  + -->
  <nodedef name="ND_blackbody" node="blackbody" nodegroup="pbr" doc="Returns the radiant emittance of a blackbody radiator with the given temperature.">
  <input name="temperature" type="float" value="5000.0" />
  - <output name="out" type="float" />
  + <output name="out" type="color3" />
  </nodedef>
  <!--
  