Fix Command.takes_count

Before, what this actually did was checking the .count argument of
a string (the *keys* in self._qute_args). Therefore, it always returned True as
soon as a command had any @cmdutils.argument decorator.

qutebrowser/commands/command.py

@@ -537,7 +537,10 @@ class Command:
 
     def takes_count(self):
         """Return true iff this command can take a count argument."""
-        return any(arg.count for arg in self._qute_args)
+        count_values = [usertypes.CommandValue.count,
+                        usertypes.CommandValue.count_tab]
+        return any(info.value in count_values
+                   for info in self._qute_args.values())
 
     def register(self):
         """Register this command in objects.commands."""