Re: Support for undo-amalgamate in a version of the atomic-change-group macro (with patch)

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Here is an updated patch with a separate macro to amalgamate undo barriers.

Looks pretty good, thanks.
I was about to install it into `master` but noticed the following:

- You seem not to have signed copyright paperwork yet.  If you're OK
  with it, please fill the form below and send it to the FSF so they can
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  [ The change is sufficiently small that we can accept it right away,
    but since the paperwork process takes some time, it's good to do it
    "in advance" so it's out of the way for your next contributions.  ]

- I see the macro binds undo limits, but AFAICT this is an "accident"
  resulting from copy&pasting code from the other macro: for the
  atomic-change macro it's very important that undo info is not thrown
  away since the macro uses the undo info internally to cancel changes
  on error, but for this macro I can't see any harm in having the undo
  info truncated, so I think we shouldn't change the undo limit
  vars.  WDYT?


        Stefan