Extrusion node fixes

Extrusion is now compliant with NIST test suite. Only texturing remains broken, so test-texture.x3d from NIST test suite is not properly rendered.

When Extrusion node was introduced, few geometries did not render at all or were rendered incorrectly. This pull request tries to fix such problems. Fix was tested with NIST test suite, so I hope it is OK and does not introduce any bug.

Anyway, textures are still mapped incorrectly as they also were before this pull request. I think to fix textures mapping, Extrusion must be internally divided to three separate units when textures applied (begin cap, end cap, trunk).