use a globally unique id when creating new Pidgin::DisplayItem's
Use a globally unique id when creating new `Pidgin::DisplayItem`s as the doc demands and as discussed on [discourse](https://discourse.imfreedom.org/t/how-is-pidgin-id-supposed-to-be-unique/134/2)
Testing Done:
Ran Pidgin and opened a conversation.
Reviewed at https://reviews.imfreedom.org/r/2980/
/*
* finch
*
* Finch is the legal property of its developers, whose names are too numerous
* to list here. Please refer to the COPYRIGHT file distributed with this
* source distribution.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1301 USA
*/
#include<glib/gi18n-lib.h>
#include<purple.h>
#include<gnt.h>
#include"gntprefs.h"
#include"gntrequest.h"
#include<string.h>
staticstruct{
GList*list_data;/* Data to be freed when the pref-window is closed */