Drop event listener exceptions on the floor.

We get a lot of failures from assertions that event listeners haven't
thrown exceptions. As the FIXME above these assertions suggests, we
should just drop them on the floor.
auto merge of #2582 : zwarich/servo/drop-exceptions, r=jdm

We get a lot of failures from assertions that event listeners haven't
thrown exceptions. As the FIXME above these assertions suggests, we
should just drop them on the floor.
Upgrade Rust.
auto merge of #2538 : mozilla/servo/rustup-20140528, r=SimonSapin

Not yet ready for merge, but you can start reviewing.

Still need to fix linux and some make check code.