Issue 3701 no oncancel

@6a68 and @seanmonstar - yo, yesterday's onmatch "fix" broke "oncancel". I fixed the fix, and added a Selenium test.

I think it would behoove us to create some specialized selenium tests to exercise the various callbacks.

Ah yes, an ephemeral instance "https://no-oncancel.personatest.org" is available to test against.

fixes #3701