core: add pointer in some callbacks (closes #406)

This pointer is the first argument received by callbacks, and the
existing argument "data" is now automatically freed by WeeChat when the
object containing the callback is removed.

With this new pointer, the linked list of callbacks in scripts has been
removed. This will improve speed of scripts (using a lot of hooks),
reduce memory used by scripts and reduce time to unload scripts.

Following functions are affected in the C API:

* exec_on_files
* config_new
* config_new_section
* config_new_option
* hook_command
* hook_command_run
* hook_timer
* hook_fd
* hook_process
* hook_process_hashtable
* hook_connect
* hook_print
* hook_signal
* hook_hsignal
* hook_config
* hook_completion
* hook_modifier
* hook_info
* hook_info_hashtable
* hook_infolist
* hook_hdata
* hook_focus
* unhook_all_plugin
* buffer_new
* bar_item_new
* upgrade_new
* upgrade_read

src/plugins/lua/weechat-lua-api.h

@@ -24,10 +24,12 @@
 extern struct luaL_Reg weechat_lua_api_funcs[];
 extern struct t_lua_const weechat_lua_api_consts[];
 
-extern int weechat_lua_api_buffer_input_data_cb (void *data,
+extern int weechat_lua_api_buffer_input_data_cb (const void *pointer,
+                                                 void *data,
                                                  struct t_gui_buffer *buffer,
                                                  const char *input_data);
-extern int weechat_lua_api_buffer_close_cb (void *data,
+extern int weechat_lua_api_buffer_close_cb (const void *pointer,
+                                            void *data,
                                             struct t_gui_buffer *buffer);
 
 #endif /* WEECHAT_LUA_API_H */