bug#10758: thumbs and image-dired to use built-in ImageMagick

[Stefan Kangas <stefan@marxist.se>]

Stefan Kangas <stefan@marxist.se> writes:

>> Glenn Morris <rgm@gnu.org> writes:
>>
>>> thumbs.el and image-dired.el both rely on using external ImageMagick
>>> utilities to resize/rotate images.
>>>
>>> If Emacs was compiled with ImageMagick support, then images of
>>> type imagemagick can be resized and rotated internally (see
>>> image-transform-*). These modes should use the internal support if
>>> it exists.
>>
>> So now that we have native image rotation and ImageMagick is on its
>> way to become deprecated, I assume that this bug should be taken to
>> mean that we want to use the built-in support here instead.

I fixed this in `image-dired' (see separate patch).

I guess we could rebase thumbs.el to also use the built-in image viewing
support, but I took a look and this external conversion seems built into
the foundation of how that library works.  So this looks to me like it
would amount to a rewrite of thumbs.el.  I could be wrong of course, but
that was my conclusion after poking at it for an hour or so.

Furthermore, at this point, image-dired.el is by far the more powerful
package, and it seems better implemented overall.  Although it borrows
heavily from thumbs.el (or at least it used to), thumbs.el seems fully
redundant these days.  However, it has some features that image-dired.el
does not, especially when it comes to modifying images.

So rather than attempting a rewrite of thumbs.el, the better solution
seems to me to add any important missing features from thumbs.el to
image-dired.el, and then obsoleting the former (not necessarily in that
order, but either way is fine to me).