Adding IE9 Compatability to xmlHTTPRequests

Haxe currently does not support cross-domain xmlHTTPRequests when it comes to IE9. 
The process of doing these requests requires a few steps that need to happen when it comes to IE9. 
The main filter that allows us to test for IE9 and similar browsers is the typeof XDomainRequest test. This allows us to only publish these changes for IE9 and browsers that use a similar protocol.

I will be using this version of these two files in my own haxe environment. I'm not sure if this is something you want to include in your master release but I highly recommend we at least work together to publish an IE9 fix for Haxe. I myself am not too familiar with Haxe code itself so the code may or may not be as clean as it should.

Thoughts?