Change the settings <key> to <raw_value> of an instance
            named <instance_name>.  <raw_value> should be a string and
            is properly converted.

def change_setting(self, instance_name, key, raw_value):
        """ Change the settings <key> to <raw_value> of an instance
            named <instance_name>.  <raw_value> should be a string and
            is properly converted. """
        ii = self.insts[instance_name]
        mo = self.modules[ii.module]
        if key in mo.deps:
            if raw_value not in self.insts:
                raise ValueError("No such instance %s" % raw_value)
            vii = self.insts[raw_value]
            vmo = self.modules[vii.module]
            if not (mo.deps[key].type in vmo.inherits or
                    mo.deps[key].type == vii.module):
                raise ValueError("%s isn't a %s" % (
                    raw_value, mo.deps[key].type))
            value = vii.object
        elif key in mo.vsettings:
            value = self.valueTypes[mo.vsettings[key].type](
                raw_value)
        else:
            raise ValueError("No such settings %s" % key)
        self.l.info("Changing %s.%s to %s" % (instance_name,
                                              key,
                                              raw_value))
        ii.settings[key] = value
        ii.object.change_setting(key, value)