MFC r208881: sh: Pass through SIGINT if interactive and job control

MFC r208881: sh: Pass through SIGINT if interactive and job control
is enabled.

This already worked if without job control.

In either case, this depends on it that a process that terminates due to
SIGINT exits on it (so not with status 1, or worse, 0).

Example:
  sleep 5; echo continued
This does not print "continued" any more if sleep is aborted via ctrl+c.

git-svn-id: svn://svn.freebsd.org/base/stable/8@210616 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f