Fix xhr abort test.
Fix xhr abort test.

Need to be more creative about ensuring that onreadystatechange is
called, but that the test conditions execute after that the function
(that does nothing...) is called.

MithrilJS/mithril.js,impinball/mithril.js,MithrilJS/mithril.js,lhorie/mithril.js,tivac/mithril.js,pygy/mithril.js,tivac/mithril.js,lhorie/mithril.js,barneycarroll/mithril.js,impinball/mithril.js,barneycarroll/mithril.js,pygy/mithril.js