wxUniversal fixes:

window.cpp's WM_CLOSE now calls Close() for wxUniv, else dialogs/
frames won't get closed using system menu/button.
Added missing NULL init for m_artProvider in themes to cure crash
Added 2 sample dsp files for wxUniv (not ideal perhaps but
it will save these getting lost, and much user frustration)


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15231 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/window.cpp

@@ -2338,10 +2338,18 @@ long wxWindowMSW::MSWWindowProc(WXUINT message, WXWPARAM wParam, WXLPARAM lParam
             break;
 
         case WM_CLOSE:
+#ifdef __WXUNIVERSAL__
+            // Universal uses its own wxFrame/wxDialog, so we don't receive
+            // close events unless we have this.
+            Close();
+            processed = TRUE;
+            rc.result = TRUE;
+#else
             // don't let the DefWindowProc() destroy our window - we'll do it
             // ourselves in ~wxWindow
             processed = TRUE;
             rc.result = TRUE;
+#endif
             break;
 
         case WM_SHOWWINDOW: