libbb: revent previous version of "concurrent history updating"

libbb: revent previous version of "concurrent history updating"
and replace it with one which does not "snoop" history written
by others. (1) it is what bug 185 needs, and (2) it is less bloaty:

function                                             old     new   delta
load_history                                           -     252    +252
read_line_input                                     3155    3287    +132
next_token                                           914     918      +4
qrealloc                                              36      33      -3
getoptscmd                                           713     708      -5
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(add/remove: 1/0 grow/shrink: 2/2 up/down: 388/-8)            Total: 380 bytes