Return `name` prepended with correct prefix.

        If the name is already prefixed, the prefix may be translated
        to the value obtained from `self.module_prefixes`.  Unmodified
        `name` is returned if we are inside a global grouping.

def add_prefix(self, name, stmt):
        """Return `name` prepended with correct prefix.

        If the name is already prefixed, the prefix may be translated
        to the value obtained from `self.module_prefixes`.  Unmodified
        `name` is returned if we are inside a global grouping.
        """
        if self.gg_level: return name
        pref, colon, local = name.partition(":")
        if colon:
            return (self.module_prefixes[stmt.i_module.i_prefixes[pref][0]]
                    + ":" + local)
        else:
            return self.prefix_stack[-1] + ":" + pref