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/common/effects.cpp

@@ -102,7 +102,7 @@ bool wxEffects::TileBitmap(const wxRect& rect, wxDC& dc, const wxBitmap& bitmap)
     }
 #endif // wxUSE_PALETTE
 
-    dcMem.SelectObject(bitmap);
+    dcMem.SelectObjectAsSource(bitmap);
 
     int i, j;
     for (i = rect.x; i < rect.x + rect.width; i += w)