dix: make DeleteCallbackList() non-static and document it

Allow using it by other places outside this file, so we can also support
callback lists in dynamically allocated structures:

Those cases need to explicitly call DeleteCallbackList() before free()ing
the structures - otherwise we're getting heap corruptions, because the
actual deletion can happen asynchronously.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

dix/callback_priv.h

@@ -10,4 +10,15 @@
 void InitCallbackManager(void);
 void DeleteCallbackManager(void);
 
+/*
+ * @brief delete a callback list
+ *
+ * Calling this is necessary if a CallbackListPtr is used inside a dynamically
+ * allocated structure, before it is freed. If it's not done, memory corruption
+ * or segfault can happen at a much later point (eg. next server incarnation)
+ *
+ * @param pcbl pointer to the list head (CallbackListPtr)
+ */
+void DeleteCallbackList(CallbackListPtr *pcbl);
+
 #endif /* _XSERVER_CALLBACK_PRIV_H */