Add api for storing a reference of a non-toxic XmlHttpRequest before implementation

[LongLiveCHIEF]

there are enough reasons where the modification of ALL requests might not be wanted, especially for extremely large SPA's.

When xhook/xdomain are initiated, create/clone so one instance uses the postMessage api, and the other uses default behavior, which can be configured through the xdomain setup. (suggesting an enhancement for that api based on this).

[jpillora]

Already done :)

https://github.com/jpillora/xhook/blob/gh-pages/src/xhook.coffee#L146

So xhook.XMLHttpRequest is the original native class, this is just a documentation issue

[LongLiveCHIEF]

sweet!