Coro crash running specs

[Charles Oliver Nutter]

I'm fixing what looks to be bugs in the coroutine-based Fiber impl,
but I saw this crash today. I think it's a result of an exception
being raised from inside the coroutine.

https://gist.github.com/1447787

To reproduce:

* clone JRuby
* ant jar install-gems fetch-stable-specs
* jruby spec/mspec/bin/mspec ci -T--1.9 -T-X-C
-T-Xfiber.coroutines=true spec/ruby/core/fiber

I saw that OpenJDK is using JIRA now...I wonder if coro could get a
JIRA project for issues?

- Charlie