Specify __exposedProps__ for xmlhttprequester.
Specify __exposedProps__ for xmlhttprequester.

Fixes #1607
Refs #1595

Ventero/greasemonkey,Martii/greasemonkey,the8472/greasemonkey,Ventero/greasemonkey,HasClass0/greasemonkey,Martii/greasemonkey,the8472/greasemonkey,HasClass0/greasemonkey