Maximum Call Stack Exceeded When Destroying a nested model

As reported by @thecountofzero [here](https://github.com/bitovi/canjs/pull/324#issuecomment-21690727) issue #324 doesn't seem to be completely fixed. Demos:

http://jsfiddle.net/thecountofzero/a2b3S/
http://jsfiddle.net/thecountofzero/8KX4N/7/

Here is the post on the forum:

http://forum.javascriptmvc.com/#Topic/32525000001308005