[PATCH] When another gajim instance is running, show roster if possible
Bug description
Ever since I remember, when you try to start gajim with another instance already open, you get the "Another instance of Gajim seems to be running. Run anyway?" dialog.
A lot of the times, you click on the gajim icon because you want to access gajim. Maybe it is hidden away in the tray by the OS (kde/win), or maybe you have no tray icon (unity...), or maybe you find it quicker to just click on the gajim shortcut.
This patch adds a new dbus-callable method, "show_roster", which is just the show part of the toggle_roster_appearance method, and adds a small test whenever gajim finds another instance already running, if gajim can tell the running instance to show_roster, it does it and exits, instead of presenting the "Run anyway dialog?".
If for some reason it doesn't work, it falls back to the old dialog, so it doesn't interfere at all with systems with no dbus or dbus issues.
Hope it is acceptable!