hush: support "! cmd | cmd" negation

function                                             old     new   delta
done_word                                            749     791     +42
run_list                                            1821    1859     +38
checkjobs                                            334     351     +17
done_pipe                                             61      74     +13
static.reserved_list                                 132     144     +12
initialize_context                                    53      45      -8
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(add/remove: 0/0 grow/shrink: 5/1 up/down: 122/-8)            Total: 114 bytes

6 files changed