Added wxMemoryDC::SelectObjectAsSource() and make SelectObject() unshare

the bitmap to ensure that no other bitmaps are modified; also remove some code
duplication by introducing wxMemoryDCBase (patch 1580745)


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42755 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/splash.cpp

@@ -149,7 +149,7 @@ static void wxDrawSplashBitmap(wxDC& dc, const wxBitmap& bitmap, int WXUNUSED(x)
     }
 #endif // USE_PALETTE_IN_SPLASH
 
-    dcMem.SelectObject(bitmap);
+    dcMem.SelectObjectAsSource(bitmap);
     dc.Blit(0, 0, bitmap.GetWidth(), bitmap.GetHeight(), & dcMem, 0, 0);
     dcMem.SelectObject(wxNullBitmap);