fix unit-tests to avoid false-positives in IE8

As discussed at #456 , this pull-request fixes the core.html unit tests to reduce false-positives in IE8 (and also one in IE10). Some of the unit tests still fail in IE8, but I think the remaining ones are actual problems in the crafty code, not just bad tests. I ran the tests and they all pass in IE10, IE9 mode (in IE10), chromium, firefox, and grunt (phantomjs).

(This is a re-do of https://github.com/craftyjs/Crafty/pull/553 after incorporating the suggestions.)