Bug 585591 – Starting/stopping drives

Add API for starting/stopping drives. This new API will enable
GVolumeMonitor and GVfs implementations to add support for the
following features

 1. Powering down external hard disk enclosures / drives

 2. Starting/stopping multi-disk devices (such as RAID/btrfs/ZFS)

 3. Connecting/disconnecting iSCSI devices

 4. Reacting to the user pressing e.g. the "remove drive" button on
    a IBM/Lenovo Ultrabay: http://www.thinkwiki.org/wiki/Ultrabay

See the bug for the corresponding GVfs and Nautilus changes.

gio/gvolumemonitor.h

@@ -117,6 +117,10 @@ struct _GVolumeMonitorClass
   void      (* drive_eject_button)   (GVolumeMonitor *volume_monitor,
                                       GDrive         *drive);
 
+  /* signal added in 2.21 */
+  void      (* drive_stop_button)   (GVolumeMonitor *volume_monitor,
+                                     GDrive         *drive);
+
   /*< private >*/
   /* Padding for future expansion */
   void (*_g_reserved1) (void);
@@ -125,7 +129,6 @@ struct _GVolumeMonitorClass
   void (*_g_reserved4) (void);
   void (*_g_reserved5) (void);
   void (*_g_reserved6) (void);
-  void (*_g_reserved7) (void);
 };
 
 GType           g_volume_monitor_get_type             (void) G_GNUC_CONST;