Sorry for the pull request to a non master branch; I figured this branch had become a de facto master for a little bit, so I didn't want to push to it directly.

Fixes included here:

• Added some calls to destructors for deques where appropriate.
• Changed an external call to gc_marks to a call to gc_mark_parallel (was causing mark_defer to be called prior to queue initialization)
• Added a VERY simple Ruby script for debugging purposes (there's probably a benchmark like this extant somewhere, but I couldn't find it). Currently, when I run this script using miniruby, I get the following stacktrace: https://gist.github.com/4067580