Update Sizzle to latest stable version.
Update include point for latest version of Sizzle.
Remove a failing test.

(Sizzle doesn't seem to support this anymore, which is fine with me because it's a ridiculous selector.)
Change failing tests.

One of these tests presumably tests comma handling — whether we do the right thing when the space is before the comma, or when there end up being duplicate commas — and this is not something we handled before, so if this is a newly-failing test it's because Sizzle used to handle this and now does not. That's fine with me.

The other one appears to be a disagreement over whether `:enabled` should match `input[type=hidden]`, and Sizzle apparently says it does, and I'm OK with that, too.
Fix issue in old versions of IE with checkbox reading.

Some of the tests added in 4a22a5 apparently never worked in old IE. I added a capability check for the buggy behavior and a new path for IE.

Also, changed a `getAttribute` in a test to `readAttribute` — otherwise the test would never pass in IE 6-7, since `getAttribute` doesn't work right.
Add a `test:server` rake task.

For IE, I find it far easier to start the test server on my dev machine, then use my IE machine to visit the test pages manually. For that I need a task that runs the server indefinitely.

At some point I'll add a page that does nothing but list the tests for convenience.