This tool allows to change the primary group for a child process.
The new primary group MUST be part of the supplementary group list
of newgrp's user token.
The command started as child process is specified on the command line.
If it's missing, start the user's default shell with the new primary
group.
TODO: Implement '-' option.
Add command description to documentation.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
c8ddd03cb0