Bug 158725 - free linked list with data

Add some helpers for freeing a linked list along with its elements by
providing a GDestroyNotify to call on each of them.

Add a test.

Based on a patch from Cosimo Cecchi.

glib/gslist.c

@@ -186,6 +186,24 @@ g_slist_free_1 (GSList *list)
   _g_slist_free1 (list);
 }
 
+/**
+ * g_slist_free_full:
+ * @list: a pointer to a #GSList
+ * @free_func: the function to be called to free each element's data
+ *
+ * Convenience method, which frees all the memory used by a #GSList, and
+ * calls the specified destroy function on every element's data.
+ *
+ * Since: 2.28
+ **/
+void
+g_slist_free_full (GSList         *list,
+		   GDestroyNotify  free_func)
+{
+  g_slist_foreach (list, (GFunc) free_func, NULL);
+  g_slist_free (list);
+}
+
 /**
  * g_slist_append:
  * @list: a #GSList