Add a new -o option to tell xargs(1) to reopen /dev/tty as stdin in

Add a new -o option to tell xargs(1) to reopen /dev/tty as stdin in
the child process, before executing the command.  This is very useful
when you do stuff like ``find ... | xargs interactive_application''.
Without -o, the application would inherit the pipe as its stdin, and
you thus lose any control over it.

This flag has been carefully chosen to not conflit with other options
of other xargs utilities like GNU xargs.

Reviewed by:	jmallett