I think this is a good solution for several reasons:

1. It does not require a new key binding, and it does not overly
   complicate the calling convention of the current key binding.

2. It turns image-rotate into a general image-rotating subroutine,
   which users and library authors alike can reuse.

2.1. It does not limit rotations of imagemagick images to multiples of
     90 degrees.

and I don't see any drawbacks, so I would like to push this to master,
subject to comments/objections.

Thanks,

-- 
Basil