pstree shows threads correct names.

pstree would only show the process name, not the thread name. This
change now makes pstree read /proc/<PID>/task/<TID>/stat to find the
threads' real names.
$ pstree -p 1187
udisksd(1187)─┬─{udisksd}(1189)
              ├─{udisksd}(1191)
              ├─{udisksd}(1192)
              ├─{udisksd}(1195)
              └─{udisksd}(27395)
./pstree -p 1187
udisksd(1187)─┬─{cleanup}(1195)
              ├─{gdbus}(1191)
              ├─{gmain}(1189)
              ├─{pool}(27395)
              └─{probing-thread}(1192)

References:
  https://sourceforge.net/p/psmisc/bugs/57/

This fix was made a lot easier due to Mapk providing a small test script
showing the broken behaviour, thanks!
Update for 22.21

Updated the translation files
Minor fix in killall man page