image/x-nikon-nrw and image/x-samsung-srw are not valid mimeTypes according
to QMimeDatabase. See also https://phabricator.kde.org/D27865
Extend documenttest to check the mimetypes returned by MimeTypeUtils::imageMimeTypes().
Re-enable documentest and remove the redundant exiv2/exif.hpp #include
to fix the build, it seems it's not needed.