ShowWithoutActivating fix for OS X Cocoa, and also add support for shaped windows...

ShowWithoutActivating fix for OS X Cocoa, and also add support for shaped windows at least when the image being drawn has proper alpha/mask set. I'm not sure if we can support it by setting a region on the TLW, as the way to do this in Cocoa is just to make the TLW's background transparent and use alpha in whatever you draw.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62656 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775