replaced wxWindowGTK::m_isStaticBox with a virtual function and replaced 3 occurences of the code finding the window for the mouse events with one

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15716 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/statbox.cpp

@@ -58,12 +58,7 @@ bool wxStaticBox::Create( wxWindow *parent,
         return FALSE;
     }
 
-    m_isStaticBox = TRUE;
-
-    if (label.empty())
-        m_widget = gtk_frame_new( (char*) NULL );
-    else
-        m_widget = gtk_frame_new( m_label.mbc_str() );
+    m_widget = gtk_frame_new(m_label.empty() ? (char *)NULL : m_label.mbc_str());
 
     m_parent->DoAddChild( this );