Force the native fields onto the POPUP_LAYER to ensure they're above everything.

This may very well not change anything, but is an experiment to see if this fixes some of our cases where fields appeared to be drawn behind (or possibly not at all) on certain machines.

And really, this is just more correct anyway.
Fix a bug where the window size was larger than requested on some platforms/themes.

Fancier Windows Vista/7 themes change the size of the window borders based on resizability of the window so we need pack() to happen last.