Solidify modifier: Add new option "Flip Normals"
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This patch adds a new option "Flip Normals" to solidify modifier. It makes normals pointing to the inside by swapping original faces and generated faces, and allows us to easily setup the backface polygons used for toon edge rendering.

I have already posted another patch for the same purpose:

but I think this patch is better way to do that, because the previous one changes the existing behavior while this one doesn't.



Uploaded a screenshot Solidify_Modifier_Flip_Normals.png .

Note that I applied another patch (GLSL mode BackFace Culling) to preview the toon edges in 3D view:


Refreshed the patch (offsets).
Also uploaded a sample .blend file which was used for the screenshot above. Please type alt+A or ctrl+F12 to preview/render the animation.

The "GLSL mode BackFace Culling" patch has been applied in r47003, so now we can preview the toon edges using "Flip Normals" option without another patch!
However, to use this option to render realtime toon edges in game engine, we have to fix a bug that solidify modifier doesn't work when material index offset is not equal to 0:

applied to svn r47039 - I made edits myself infact but they ended up being so similar to your patch that I added you as contributor.

Thanks for the apply! Confirmed it works fine.