use 6px as the default wxSizer border in wxGTK to be a little bit closer to GNOME HIG

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52356 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/sizer.h

@@ -84,9 +84,15 @@ public:
     static int GetDefaultBorder()
     {
 #if wxUSE_BORDER_BY_DEFAULT
+    #ifdef __WXGTK20__
+        // GNOME HIG says to use 6px as the base unit:
+        // http://library.gnome.org/devel/hig-book/stable/design-window.html.en
+        return 6;
+    #else
         // FIXME: default border size shouldn't be hardcoded and at the very
         //        least they should depend on the current font size
         return 5;
+    #endif
 #else
         return 0;
 #endif