Bug#717818: Implemented for multiple image formats, except .ICO

[Felix Lechner <felix.lechner@lease-up.com>]

Hi Helmut,

> Please issue a message for each file, that has PNG contents, but is not
> named *.png or *.PNG.

A new check covers several image formats and names:

    https://salsa.debian.org/lintian/lintian/commit/12b81f00021fc7ded44388125e763a179bbd794e

> The tag should likely be pedantic

There are two tags. The standard one is pedantic.

> maybe some extensions such as .ico, .gif, .jpg, .jpeg, .pbm
> .tiff, .xpm could raise the tag to something normal

This is where the second tag comes in. Image files whose names suggest
another format are misleading. They are tagged at the slightly higher
severity wishlist. It works across all formats, not just PNG.

I did not implement .ICO because it is, or has evolved into, a
container format that can also contain PNG images.

Kind regards
Felix Lechner