[PATCH 1 of 4] histedit: add a method to cleanup nodes safely

[Jun Wu]

Excerpts from Yuya Nishihara's message of 2017-03-18 11:48:30 +0900:
> (+CC Pierre-Yves)

I guess he may be busy with other stuffs.

> I meant they both could be iterators/generators now, but 'sucs' wouldn't
> be by design. I'm saying that because it seems not common to take a nested
> iterator as an argument.

I'll send a non-generator version.