MFC r311268:

MFC r311268:

Clarify lifetime of child(..) function

Ensure child exits when complete as it's always run in a forked
process.

Add a missing break statement in :pselect_sigmask when calling
child(..) for clarity and to avoid weird domino effects if the
child process somehow does something it's not supposed to do
with the logfiles, file descriptors, etc

CID:		1223369, 1223370, 1300301

git-svn-id: svn://svn.freebsd.org/base/stable/10@312039 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f