Fix is for browser support in IE < 9

This is exposed by the prototypes when running from IE 8 (or earlier) and is from some really old code from TCDriver. Bit of a miracle it hasn't been exposed until now. In practice this change is exercised by the request complete function in LRS' sendRequest method for IE cross domain requests, but it should be safe to shim the global with this fix which will only happen when something else hasn't already shimmed it. Will test as part of prototypes update, but need upstream merge first. (Some day [soon] we'll have better unit tests.)