Resize event not emitted on windows 7

Hey,

i noticed that the resize event is not emitted on windows 7.

``` go
66 ui.Handle("/sys/wnd/resize", func(e ui.Event) {
[...]
73 })
```

The program was compiled on OSX with `GOOS=windows GOARCH=386 go build prog.go`
and started on windows 7 with the default system shell.
As a workaround I start a timer and poll the terminal size and update the view if required.

Regards,
Ruben

Start at the `/sys/wnd/resize` handler shown in the report and reproduce the behavior using the stated GOOS=windows GOARCH=386 build on Windows 7 with the default system shell. The issue is done when resizing the terminal emits the resize event without requiring polling.

Written by the indexing model from the issue text.