libbb/lineedit: implement optional Ctrl-R history search

function                                             old     new   delta
read_line_input                                     3433    3957    +524
load_string                                           77      90     +13
input_tab                                           1086    1069     -17
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(add/remove: 0/0 grow/shrink: 2/1 up/down: 537/-17)           Total: 520 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2 files changed