Fix #68 bug windows scale

[joao-bolsson]

File Dock.java contains a demo which can test the bug, following the steps: (With 2 displays and Windows 10)

Open "display settings" in Windows and put:

Main display: 100%
Second display: 125%

1. Run Dock.java
2. Externalize one of the colors and drag to the other display (the one with zoom 125%)
3. Maximize the dragged window.

Result: it'll work fine, now, test without the changes: it won't work.

There are some others bugs like when resizing the externalized and maximized dock (the mouse doesn't run together with the border). I believe that it can be solved as well.

[Benoker]

Thanks. I'll just pick and copy the interesting parts from your pull request :-)

I have ordered a second monitor for myself, and I would like to try out your solution with it. Unfortunately the delivery date gets pushed back (every week I get a mail with the message "your monitor will be delivered in 2 weeks"....). So I might delay integration of your code until the monitor arrived.