Scrolling in doc-view

[Chong Yidong <cyd@stupidchicken.com>]

The newly-installed doc-view package doesn't properly handle images
that are wider or taller than the Emacs window.  The left/right keys
don't scroll the image horizontally, and scrolling vertically is
cumbersome (because once you reach the bottom of the image, it
disappears without warning, whereupon trying to scroll back up jumps
back to the top of the image).

Image-mode used to have the same problems, but I recently enhanced it
so that large images can be scrolled vertically and horizontally.  It
would be good to avoid re-introducing these annoyances with doc-view
mode.  Could you take a look at the relevant functions in
image-mode.el (image-forward-hscroll, image-backward-hscroll,
image-previous-line, image-next-line, etc.) and try to use them in
doc-view mode?

Thanks.