Injects a vbscript tag containing a 'getIEByteArray' method for reading
binary data from an xhr response in IE8 and below.
@private
function() {
        var scriptTag = document.createElement('script');
        scriptTag.type = 'text/vbscript';
        scriptTag.text = [
            'Function getIEByteArray(byteArray, out)',
                'Dim len, i',
                'len = LenB(byteArray)',
                'For i = 1 to len',
                    'out.push(AscB(MidB(byteArray, i, 1)))',
                'Next',
            'End Function'
        ].join('\n');
        Ext.getHead().dom.appendChild(scriptTag);
        this.self.vbScriptInjected = true;
    }