Work around stupid error in Minefield.

common/modules/base.jsm

@@ -1000,7 +1000,9 @@ var ErrorBase = Class("ErrorBase", Error, {
     level: 2,
     init: function EB_init(message, level) {
         level = level || 0;
-        update(this, Error(message))
+        let error = Error(message);
+        update(this, error)
+        this.stack = error.stack;
         this.message = message;
 
         let frame = Components.stack;

common/modules/commands.jsm

@@ -1425,11 +1425,8 @@ var Commands = Module("commands", {
                                     return context.completions = result;
                             };
                         }
-                        else {
-                            util.assert(set.has(config.completers, completer),
-                                        _("command.unknownCompleter", completer));
+                        else
                             completerFunc = function (context) modules.completion.closure[config.completers[completer]](context);
-                        }
                     }
 
                     let added = args["-group"].add(cmd.split(","),