irc: fix separator between nick and host in bar item "irc_nick_host"

Use "!" instead of "@" to separate nick from host, like it is done in IRC
protocol.

The nick and host is now displayed as "nick!user@host" instead of
"nick@user@host".

ChangeLog.adoc

@@ -39,6 +39,7 @@ Bug fixes::
   * core: do not remove quotes in arguments of command /eval as they can be part of the evaluated expression/condition (issue #1601)
   * core: display an error when the buffer is not found with command /command -buffer
   * buflist: add option buflist.look.use_items to speed up display of buflist (issue #1613)
+  * irc: fix separator between nick and host in bar item "irc_nick_host"
   * irc: fix completion of commands /halfop and /dehalfop
 
 Documentation::

src/plugins/irc/irc-bar-item.c

@@ -472,7 +472,7 @@ irc_bar_item_nick_host (const void *pointer, void *data,
 
     snprintf (buf, sizeof (buf), "%s%s%s",
               server->nick,
-              (server->host) ? "@" : "",
+              (server->host) ? "!" : "",
               (server->host) ? server->host : "");
 
     return strdup (buf);