dojo.gfx 3d proof-of-concept implementation

This is the first proof-of-concept implementation of dojo.gfx 3d support. Just copy test3d.html to $dojo/trunk/tests/gfx/, and launch any SVG-based browser, Mozilla Firefox is preferred, and you would found a cube like this:

Cube SVG
Cube SVG

This is a quite quick-n-dirty implementation, the Path3d class is more or less a hybrid of dojo.gfx.Path and dojo.gfx.path.Path, operations are copied from here and there with modification to meet our needs. The main contribution of this test is

We are probably inspired by this lousy implementation for its weakness:

I think I need to consult with my mentor for more details about refactoring.