libtorrent-rasterbar 1.1.* (packaged here as libtorrent-rasterbar-
legacy) is ABI incompatible with libtorrent-rasterbar-1.2.*. It is made
available here because it is a build and run time dependency for
qBittorrent.

In summary: If you would like to install an older version of qBittorrent
or tribler built with qt4, install this package.  If you would like to
install qbittorrent-qt5, then do not install this package. Instead,
install libtorrent-rasterbar.
