fix CMake config file version compatibility

[FranciscoPombal]

Make it the application's responsibility to manage their supported
versions.

This can be done with CMake find_package() version ranges, for instance.

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Context: qbittorrent/qBittorrent#13510 (comment) and the following two comments below it. An application like qBittorrent might want to support two or more versions at the same time that differ in major and minor version. It is difficult to accomplish this with the SameMinorVersion restriction in the generated CMake config files.

[FranciscoPombal]

This is meant to be merged into RC_2_0 and master as well, of course.

[zywo]

@FranciscoPombal
Just tested and works as expected with this command:
cmake -DLibtorrentRasterbar_DIR=~/build/rc_2_0/LibtorrentRasterbar/ ~/qbittorrent/

[FranciscoPombal]

@zywo If you install libtorrent to your standard system dirs, it should also work without manually specifying LibtorrentRasterbar_DIR (but I think you already know this).

[zywo]

Yes, but I avoid doing sudo make install every time I compile libtorrent.

[FranciscoPombal]

EDIT: wrong issue.

[arvidn]

looks reasonable. @zeule you agree?