bug#8938: make timeout and CTRL-C

[shay shimony]

> With this patch the child is guaranteed to not be in the foreground (as far
> as the tty knows) so it will be getting SIGTTIN and possibly SIGTTOU on tty
> operations.

You may need to correct me. In practice we see that the "timeouted" program
perform successfully writes to the terminal, though it belongs to a
different group then the foreground (in my case "make"'s group is in the
foreground and timeout+compiler/test group is in the background, and all
output of the compiler and test seem to appear correctly on the terminal).
And regarding read, I think it makes sense enough that users will not use
timeout for interactive programs that wait for input from the user.
So maybe the fact that the timeouted program will not be able to get SIGTTIN
and SIGTTOU is not such a disaster?