* Added SetNSBitmapImageRep so that wxMemoryDC can update the contents by
replacing the entire NSBitmapImageRep.
* Added ability to create bitmaps from width/height
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22704 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775