build: require glib 2.28

As dieterv said, gtk 2.24 win32 binaries have been frozen on
glib 2.28.x, and we dont have resources rigth now to ensure pygobject
static bindings still function correctly with newer glib versions

configure.in

@@ -32,7 +32,7 @@ m4_define([gtk_api_version], [2.0])
 m4_define([gtk_binary_version], [2.10.0])
 
 # required versions of other packages
-m4_define([glib_required_version], [2.30.0])
+m4_define([glib_required_version], [2.28.0])
 m4_define([pango_required_version], [1.20])
 m4_define([atk_required_version], [1.29.2])
 m4_define([cairo_required_version], [1.6])

gtk/gtkfilechooserdefault.c

@@ -6705,7 +6705,11 @@ file_system_model_set (GtkFileSystemModel *model,
       if (info == NULL || _gtk_file_info_consider_as_directory (info))
         g_value_set_string (value, NULL);
       else
+#if GLIB_CHECK_VERSION(2,30,0)
         g_value_take_string (value, g_format_size (g_file_info_get_size (info)));
+#else
+        g_value_take_string (value, g_format_size_for_display (g_file_info_get_size (info)));
+#endif
       break;
     case MODEL_COL_MTIME:
     case MODEL_COL_MTIME_TEXT: