Update GPGPU example

- Position textures require alpha channel to store bird's phase
- Rendertarget type should match texture size
- I don't remmeber when the birds get clotted into balls previous :S
Position texture requires alpha channel for bird phase
initialize face.vertexNormals and __tmpVertices more often, to make sure they are available when computeVertexNormals is called (again) after faces or vertices have changed.
remove __tmpVertices vertex normal cache
Merge branch 'dev' of https://github.com/martinwicke/three.js into dev