[Development] QMovie no longer supports .mng

[Kevin Kofler]

Jake Petroules wrote:
> The MNG and JPEG2000 plugins are no longer built by default on most
> platforms because upstream development has stalled and there are known
> security vulnerabilities. See
> https://codereview.qt-project.org/#/c/141429/

For libmng, you bundle the ancient version 1.0.10 from 2009 (!). The current 
version is 2.0.3 from 2015:
https://sourceforge.net/projects/libmng/files/libmng-devel/
Despite the new major version number, qt5-qtimageformats compiles with no 
changes against that version.

For JPEG2000:

> You can still build them manually if you really want them. Perhaps you
> could help port the JPEG2000 plugin to
> https://github.com/uclouvain/openjpeg

That would be an option. But I would start by just getting the Jasper 
security fixes from a GNU/Linux distribution (e.g.:
http://pkgs.fedoraproject.org/cgit/rpms/jasper.git/tree/
) and applying them to your bundled copy.

        Kevin Kofler