* Exposed Tex.use_nodes, Tex.nodetree, MTex.which_output in RNA
* Added node controls to texture buttons (Use Nodes and Use Output)
* Made new texture outputs have unique names by default, though unique names still aren't required.
Note: The preview window in the texture buttons only takes which_output into account when in "material" mode, and in the material half of "both" mode; the plain texture display ignores the user's output choice.
This is because ED_preview_draw draws a Tex* and not an MTex* -- still some work to do here.
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