[docs] [issue23006] Improve the doc and indexing of adict.__missing__.

Terry J. Reedy added the comment: I made a couple more minor revisions to the 3.4 stdtypes text and copied the revised paragraph, with the code example, to 2.7 ---------- resolution: -> fixed stage: needs patch -> resolved status: open -> closed _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23006> _______________________________________