Add support for deprecated RegExp (constructor) properties

These were apparently part of ancient EcmaScript specs, aren't even listed
anymore in any recent spec (not even as deprecated), but apparently they
are part of what the web supports as well as previous versions of Qml. So
this patch implements them.

Task-number: QTBUG-36244

Change-Id: I1b9ea7ea09fceb6a486f615837a71e41aae12de4
Reviewed-by: Lars Knoll <lars.knoll@digia.com>