Fix some glib docs warnings

Remove some symbols from glib-sections.txt that gtk-doc has no idea
about.

Add proper callback typedefs for GTester (gtk-doc dislikes inline
function types).

Fix some other minor issues.

glib/gstdio.c

@@ -425,6 +425,14 @@ g_chdir (const gchar *path)
 #endif
 }
 
+/**
+ * GStatBuf:
+ *
+ * A type corresponding to the appropriate struct type for the stat
+ * system call, depending on the platform and/or compiler being used.
+ *
+ * See g_stat() for more information.
+ **/
 /**
  * g_stat: 
  * @filename: a pathname in the GLib file name encoding (UTF-8 on Windows)