Add missing ; to last commit.
Fix cd/exit while work on pipes+jobs continues

They weren't working because the code using jobs for everything forks
the built ins. This sorta undoes that for now.
Adjust code generators handling of '|'

The commands now end up as a stack of arrays, to be passed to
exec_pipe(). exec_pipe has been renamed to exec_pipe_old() and a stub
exec_pipe() written.