MINOR: lua: export applet and task handlers

MINOR: lua: export applet and task handlers

The current functions are seen outside from the debugging code and are
convenient to export so that we can improve the thread dump output :

  void hlua_applet_tcp_fct(struct appctx *ctx);
  void hlua_applet_http_fct(struct appctx *ctx);
  struct task *hlua_process_task(struct task *task, void *context, unsigned short state);

Of course they are only available when USE_LUA is defined.