hush: ifdef out parts which are not needed

hush: ifdef out parts which are not needed
if neither loops nor ifs are supported. Code savings:

function                                             old     new   delta
parse_stream                                        1758    1757      -1
checkjobs                                            335     318     -17
done_pipe                                             74      52     -22
expand_variables                                    1437    1407     -30
run_list                                            1232    1189     -43
parse_and_run_stream                                 328     267     -61
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/6 up/down: 0/-174)           Total: -174 bytes