Fix for issue #2739

As mentioned in http://stackoverflow.com/questions/11250053/three-js-canvas-particles-dont-render-with-orthographiccamera there is a clipping problem with particles that is apparent when using the Orthographic camera. The problem is in Projector.js that clips particles to the far part of the view frustrum.

I have made a JSFiddle illustrating the problem, http://jsfiddle.net/89Pgx/1/.