tnef: 1.4.15 -> 1.4.17

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17/bin/tnef -h` got 0 exit code
- ran `/nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17/bin/tnef --help` got 0 exit code
- ran `/nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17/bin/tnef -V` and found version 1.4.17
- ran `/nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17/bin/tnef --version` and found version 1.4.17
- ran `/nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17/bin/tnef -h` and found version 1.4.17
- ran `/nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17/bin/tnef --help` and found version 1.4.17
- found 1.4.17 with grep in /nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17
- found 1.4.17 in filename of file in /nix/store/ggbdpmwgrbzr50ck27qh6pd82f2hapd8-tnef-1.4.17

cc "@peterhoeg"