Changed BorderlessWindowBehavior to use WindowChrome instead of using DWM non-client rendering directly.

Added http://archive.msdn.microsoft.com/WPFShell for MA.M .NET 4 client profile.
Fixes #481, #488, #496.
added dependency for *just* net40
moved using statements up, indicate they are related
leverage the EnableDWMDropShadow dependency property to set AllowTransparency
here's your demo
reenable drop shadow (hopefully the last fix for this)
introduced separate property for AllowsTransparency
updated Interop sample to show how you resolve the issue