More border rationalisation. GetDefaultBorder is now mostly defined in base class files.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@49893 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/button.h

@@ -78,6 +78,9 @@ public:
     static wxSize GetDefaultSize();
 
 protected:
+    // choose the default border for this window
+    virtual wxBorder GetDefaultBorder() const { return wxBORDER_NONE; }
+
     DECLARE_NO_COPY_CLASS(wxButtonBase)
 };