setsid: add an option to wait child return value

setsid: add an option to wait child return value

This change proposed in util-linux maillist by Damien Wyart in behalf of
Daniel Kahn Gillmor.  Sami Kerola changed the patch to use option rather
than makign the default behavior of the command to change.

Reported-by: Damien Wyart <damien.wyart@gmail.com>
Reference: http://markmail.org/message/2z6qh5auk7wjie3l
Bug-Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=495881
CC: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>