hush: pass $! thru re-execution; try harder on re-exec; give error

hush: pass $! thru re-execution; try harder on re-exec; give error
 msg if re-exec didn't work; other tweaks in main()

function                                             old     new   delta
hush_main                                           1144    1199     +55
re_execute_shell                                     237     286     +49
file_get                                             240     260     +20
clean_up_after_re_execute                             58      66      +8
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(add/remove: 0/0 grow/shrink: 4/0 up/down: 132/0)             Total: 132 bytes