bug#26500: [PATCH] gnu: Add mcomix.

[Arun Isaac <arunisaac@systemreboot.net>]

> Hello, here is mcomix.

Thanks for the patch!

> I tested it with zip, CBZ, 7zip pdf files, and a directory with normal
> images, they all work fine.
>
> I also tried unrar, but couldn't extract any archive with it, neither
> through mcomix, nor manually through the commandline tool, so this might
> be a separate problem.

I'm yet to actually test running the application. Will do so and get
back in a while. Meanwhile, other changes.

> +    ;; Python 2.5 or newer (Python 3 and up is not supported)
> +    (arguments `(#:python ,python-2))

You can remove the comment. It's more or less obvious from the
'arguments' section that mcomix needs python 2.

> +    (propagated-inputs `(("python2-pygtk" ,python2-pygtk)
> +                         ("gtk+" ,gtk+)
> +                         ("python2-pillow" ,python2-pillow)))

These are inputs not propagated-inputs. propagated-inputs are only
required for python libraries. For python applications such as mcomix,
the executable gets wrapped in a script which sets the correct
PYTHONPATH variable. Look at $out/bin/mcomix and $out/bin/.mcomix-real

Also, is the gtk+ dependency required? mcomix seems to build and run
fine on my system without it.

> +    (description "A customizable image viewer that specializes as
> +a comic and manga reader.  It supports a variety of container formats
> +including CBR, CBZ, CB7, CBT, LHA.

Please make this "MComix is a ... ". See
https://www.gnu.org/software/guix/manual/html_node/Synopses-and-Descriptions.html

> +    (license license:gpl2)))

This should be license:gpl2+. When no license version is explicitly
specified in the source headers, it is of the "or later" variant. See
https://lists.gnu.org/archive/html/guix-devel/2017-02/msg00026.html

Also, add a copyright header for yourself at the top of the source file
(gnu/packages/image-viewers.scm in this case).