Replace wxComboPopupEvtHandler with calls to Bind() as well

This is not as much of a simplification as the previous two commits
because there is no simple replacement of EVT_MOUSE_EVENTS() using
Bind() and a loop over all mouse event types has to be written
explicitly, but it still avoids the need to allocate and delete a
separate object, so is still worth it.

include/wx/combo.h

@@ -579,6 +579,8 @@ protected:
     void OnPopupKey(wxKeyEvent& event);
     void OnPopupSize(wxSizeEvent& event);
 
+    void OnPopupMouseEvent(wxMouseEvent& event);
+
     // Set customization flags (directs how wxComboCtrlBase helpers behave)
     void Customize( wxUint32 flags ) { m_iFlags |= flags; }
 
@@ -637,9 +639,6 @@ protected:
     // this is for the top level window
     wxEvtHandler*           m_toplevEvtHandler;
 
-    // this is for the control in popup
-    wxEvtHandler*           m_popupEvtHandler;
-
     // main (ie. topmost) window of a composite control (default = this)
     wxWindow*               m_mainCtrlWnd;
 
@@ -718,6 +717,10 @@ protected:
     // is the text-area background colour overridden?
     bool                    m_hasTcBgCol;
 
+    // flags used while popup is shown
+    bool                    m_beenInsidePopup;
+    bool                    m_blockEventsToPopup;
+
 private:
     void Init();