When no shrink is needed, two new hooks are added in this patch
with the default value containing vc-shrink-buffer to preserve
the current behavior that can be easily removed in user configuration
by e.g.:

  (remove-hook 'vc-diff-finish-functions 'vc-shrink-buffer)
  (remove-hook 'vc-log-finish-functions 'vc-shrink-buffer)