Handle disabled behavior

[andrejewski]

We should check out the disabled behavior @christopherjbaker ran into in canjs/can-util#294.

I don't know if it merits a code change here, I just want to understand the behavior and potentially normalize. I do not want to include the warning.

[chasenlehara]

@andrejewski What should be the next steps for this issue?

[andrejewski]

Not a priority, but this warning can be ported over to can-dom-events dispatch method.

I say non priority as this warning was only made necessary by our flaky can-util mutation tests. This detection may be a hack for an unrelated problem which is not evident to this project's tests.