Return the caption from wxMessageDialog::GetTitle().

It was unexpected that wxMessageDialog::GetTitle() returned empty string even
when non-empty caption, which is just another word for title, was specified.

Implement GetTitle() as synonym for GetCaption() and also provide SetTitle()
for consistency.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77741 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msgdlg.h

@@ -101,6 +101,12 @@ public:
 
     wxString GetCaption() const { return m_caption; }
 
+    // Title and caption are the same thing, GetCaption() mostly exists just
+    // for compatibility.
+    virtual void SetTitle(const wxString& title) { m_caption = title; }
+    virtual wxString GetTitle() const { return m_caption; }
+
+
     virtual void SetMessage(const wxString& message)
     {
         m_message = message;