fixing detect script to work in safari 5

Detecting support for the Event constructor is quite tricky, it turns out.

In safari 5 -7 window.Event is '[object EventConstructor]' but cannot be instantiated with the new keyword as it not actually an constructor(!)  In safari 8 it can be instantiated but is still instanceof Object, not Function(!!).  In new versions of IE it also an object but cannot be intantiated.

Therefore try/catch is only safe way to detect whether or not this works...