This is more likely to be correct, and a necessary step in case we ever want
to move to Object.is.
This keeps ise as an alias for is, and introduces is_loosely for the old
behaviour.
We are white-listing the existing set of tests that use setTimeout
like this. Hopefully these tests will be investigated and fixed
in the future, so that we can narrow down the white-list.
This check is only turned on for mochitest-plain for now.
