use TTF_TRANSPARENT to fix problem with flashing tooltips (patch 1821229)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@49510 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/tooltip.cpp

@@ -91,6 +91,17 @@ public:
         hwnd = hwndOwner;
         uFlags = TTF_IDISHWND;
 
+        // we use TTF_TRANSPARENT to fix a problem which arises at least with
+        // the text controls but may presumably happen with other controls
+        // which display the tooltip at mouse position: it can start flashing
+        // then as the control gets "focus lost" events and dismisses the
+        // tooltip which then reappears because mouse remains hovering over the
+        // control, see SF patch 1821229
+        if ( wxApp::GetComCtl32Version() >= 470 )
+        {
+            uFlags |= TTF_TRANSPARENT;
+        }
+
         uId = (UINT)hwndOwner;
     }
 };