.prototype segfaults

I like to inspect prototype attributes to get a feel for what methods objects support, but this causes segfaults on most objects, like this one:

```
$ node
> require('canvas').prototype

rlwrap: warning: node killed by signal 11 - rlwrap will now kill itself with the same signal
Segmentation fault
```

This is on node v0.2.5 and it seems that most everything else works.
