bug#42829: save-some-buffers should learn to "just let go"

[積丹尼 Dan Jacobson]

emacs-version "26.3". (maybe fixed already?)

C-x s says

  Save file ...documentation.txt? (y, n, !, ., q, C-r, d or C-h)

C-h then says

  Type SPC or ‘y’ to save the current buffer;
  DEL or ‘n’ to skip the current buffer;
  RET or ‘q’ to give up on the save (skip all remaining buffers);
  C-g to quit (cancel the whole command);
  ! to save all remaining buffers;
  C-r to view this buffer;
  d to view changes in this buffer;
  or . (period) to save the current buffer and exit.

Problem is: C-r won't "let go of the user".

He can't just visit the buffer (to say undo his changes there.)
He is still trapped at the prompt. No C-x o won't free him temporarily.

Therefore there needs to be an additional choice:

"v to just visit that file and quit saving the rest of the files if any"