Re: image-dired: Check all external programs available

[Tino Calancha <tino.calancha@gmail.com>]

On Tue, 30 Aug 2016, Mathias Dahl wrote:

>From my viewpoint, and after just a quick overview of the changes, I 
> think it looks good. If we can present more meaningful error messages
>to the user, it can only be good.
>I noticed you did a small change in the logic surrounding jpegtran; IIUC
> you fallback to use "convert" if jpegtran is not available.

As you know, 'convert' also can rotate an image. I have noticed that 
'jpegtran' is not included in the Debian repositories; 'convert' is 
in Debian rep. and is also used to create the thumbnail and the temporary 
image so it should be installed to use this lib anyway.
The default value for 'image-dired-cmd-rotate-original-options' is set
accordingly with the executable used: jpegtran or convert.

Another way could be to drop 'jpegtran' dependency and 
just set 'convert' as default value for the following three options;
image-dired-cmd-create-thumbnail-program
image-dired-cmd-create-temp-image-program
image-dired-cmd-rotate-original-program

> As long as you have tested both scenarios I'm fine with the change.
> The same goes for the other changes of course, that they are tested and 
>works well.
>Someone else has to apply this to the Emacs source code however, since 
>I'm not up-to-date
>with how commits are done these days.
I will keep testing during this week.  Then, if everything is OK
i will push the patch to the Emacs repository.
>Thanks!
Thank you very much!

Tino