Fix issue when quickly pressing Evaluate button multiple times
Add comments about previous commits
Make timeouts work with interact messages

Timeouts were broken with interacts since interacts were sending custom message types, but the timeout infrastructure was just looking for messages of type "execute_request"
An incomplete attempt at launching new kernels when evaluate is pressed (and killing the old kernel).
Ignore messages sent to killed kernels

(this was causing errors when double-clicking Evaluate)
Allow a CORS delete request to kill a kernel, and stop invalidating base_url

The base_url is important so that the kernel delete requests go to the right URL.

Why did we originally modify the base_url?
Allow fake DELETE request through form submission where XHR is not available
Fix for strict mode
Merge pull request #389 from ihanson/double-eval

Problems with quick re-evaluation