JBIDE-18042 VPE: Disabling window.confirm, window.prompt and window.open

Would it be better to have 
``` java 
browser.execute ("window.alert = function() {};" + //$NON-NLS-1$
"window.confirm = function() {};" + //$NON-NLS-1$
"window.prompt = function() {};" + //$NON-NLS-1$
"window.open = function() {};") //$NON-NLS-1$
```