Fix handling of forms in IE10.

In IE10, it seems that normal links are routed fine, but forms are not.
Minimal example: http://jsfiddle.net/xg4Hr/2/ - In Firefox and Chrome,
clicking the GET and POST buttons display "GET" and "POST" as you'd
expect. In IE10, the Davis.js routing is ignored and you get a 404
error. I narrowed the problem down to the `originChecks` function in
davis.listener.js, on this line:

    a.href = elem.action

In Firefox and Chrome, this will make `a.host` equal to the domain
name. In IE10, the port number gets stuck on the end of `a.host`, for
some reason. This makes `this.A(a)` on the next line return false since
Davis.js thinks it is an external link. I worked around this by creating
`a2` to compare with `a`.