gwenview now uses exiv2, as do some other kde pieces (so exif is probably no longer be needed for kde at all in the near future). Bump the gwenviewcore major: the cache public object now sports a nice pimpl, so the interface cannot be the same...
Recognize (and use) libmng. Make sure we recognize the correct libexif, since old stuff would not work, and advertize the upcoming i18n package...