>> there still are some minor glitches near the beginning of an Info
>> node; these are left as exercises

1. I think I fixed glitches at the beginning of Info node.  The key
   was to get height of the `unseen' and coming line above the first
   line of the current window.

2. Name of a function was not appropriate.  I found a good verb,
   `whistlestop' and renamed them.

   - `pixel--sweep-pixel-up' is renamed to `pixel--whistlestop-line-up'

I send the revised copy and the diff.  Two possible ways to test the
code are shown below.

 (require 'pixel-scroll)
 (pixel-scroll-mode 1)
 (setq pixel-resolution-fine-p t)

 (require 'pixel-scroll)
 (pixel-scroll-mode 1)
 (setq mouse-wheel-scroll-amount '(1 ((shift) . 5) ((control))))
 (setq mouse-wheel-progressive-speed nil)