two problems with GL tracing

I used http://scenejs.wikispaces.com/Logging+WebGL+Calls to track down the problem on ticket #124 0.7.6 live examples blank canvas in Chrome 5.0.375.99 . Very nice!

However, I had to make two changes to the tracing code to get it to work for me. I've attached a patch with the changes.

The first change was to comment out printing the contents of WebGLFloatArray objects that get passed to webgl. Chrome was giving errors like "WebGLFloatArray has no method .get()" (that's not the exact wording). Simply commenting out the code is presumably not the right fix; on the other hand, if you're sending a 20,000 element array to webgl, printing the whole thing might not be the best idea anyway. Maybe it should abbreviate (print only the first 10 and last 6 elements if it has more than 16 elements, for example). (Those numbers were carefully chosen so that it would print the entirety of a mat4.) The second change was to add a test for undefined where there was already a test for null. I didn't try to understand the code there; I just saw in the debugger that arg was undefined.