On OS X (tested on 10.10.5) calls to window.open() with a different target
than _self were simply ignored. No navigation and no EVT_WEBVIEW_NEWWINDOW as
expected.
Unfortunately WebKit does not call the decidePolicyForNewWindowAction delegate
method in these cases. A new delegate method createWebViewWithRequest has been
implemented to handle this case and send EVT_WEBVIEW_NEWWINDOW as in other
ports.
Closes https://github.com/wxWidgets/wxWidgets/pull/86
(cherry picked from commit e6b31adefe)