Fixed: CPWindow doesn't take the event when moving from another platformWindow

Previously, when moving from platformWindow to another platformWindow, the targeted window didn't get the new event because the keyWindow of the application was still set to the other platformWindow.

This PR fixes another issue about opening panel in a platformWindow. When opening a panel in a platformWindow, cappuccino set the new key window to the wrong platformWindow.
Merge pull request #2256 from Dogild/PlatformWindowKey

Fixed: CPWindow doesn't take the event when moving from another platformWindow