Util.killall: add utility for killing unwanted processes

Since we have to use pkill, kludgily, for the right combination of
portability and featurefulness, put the code in one place rather than
duplicating it everywhere.

https://bugzilla.gnome.org/show_bug.cgi?id=635089

js/ui/status/power.js

@@ -1,7 +1,6 @@
 /* -*- mode: js2; js2-basic-offset: 4; indent-tabs-mode: nil -*- */
 
 const Gio = imports.gi.Gio;
-const GLib = imports.gi.GLib;
 const DBus = imports.dbus;
 const Lang = imports.lang;
 const Mainloop = imports.mainloop;
@@ -196,7 +195,7 @@ Indicator.prototype = {
 
     _checkError: function(error) {
         if (!this._restarted && error && error.message.match(/org\.freedesktop\.DBus\.Error\.(UnknownMethod|InvalidArgs)/)) {
-            GLib.spawn_command_line_sync('pkill -f "^gnome-power-manager$"');
+            Util.killall('gnome-power-manager');
             Util.spawn(['gnome-power-manager']);
             this._restarted = true;
         }