Here's an updated patch for py3k (3.2).  The test still fails without the fix, and passes with the fix.

Thinking more about this, I'll try summarizing the bug more coherently:

When the main thread joins the child threads, it acquires some locks.  If a fork in a child thread occurs while those locks are held, they remain locked in the child process.  My solution is to do here what we do elsewhere in CPython: abandon radioactive locks and allocate fresh ones.