Fit image to window height or width

[Vaidheeswaran]

(See my earlier post)

I am using doc-view.el for digitizing scanned books.  I usually have
the document page span the whole of window width.  Occassionally, I
run into a page -- mostly a table and occsionally an image -- that is
in landscape format.

1. I find that `image-transform-fit-to-height' and friends apparently
   don't work.

2. I want an ablility to to transform an image that is rendered by
   doc-view mode.

(Even if image transformation is broken in the core library, it should
be doable either via "convert" command.  See image-dired.el.  AFAIK, 
shr.el also does image transformation without relying on command line.)