Merge "selected" and "active" child in wxAuiMDIParentFrame.

They are one and the same thing and so just make them really synonymous
instead of (unsuccessfully) trying to keep them synchronized.

Closes #14684.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72556 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/aui/tabmdi.h

@@ -85,7 +85,6 @@ public:
 
 protected:
     wxAuiMDIClientWindow*   m_pClientWindow;
-    wxAuiMDIChildFrame*     m_pActiveChild;
     wxEvent*                m_pLastEvt;
 
 #if wxUSE_MENUS
@@ -250,6 +249,11 @@ public:
                               long style = wxVSCROLL | wxHSCROLL);
 
     virtual int SetSelection(size_t page);
+    virtual wxAuiMDIChildFrame* GetActiveChild();
+    virtual void SetActiveChild(wxAuiMDIChildFrame* pChildFrame)
+    {
+        SetSelection(GetPageIndex(pChildFrame));
+    }
 
 protected: