Port Hare's auto-grow newscanner (scanner.ha:72) and scan_rune
(scanner.ha:259). scanner gains a maxread field (== cap for
newscannerbuf, scanner.ha:101); readahead grows by BUFSZ up to
maxread via alloc+copy (Hare appends; ww flat ptr/cap scanner,
old block left to process-exit reclaim). scanbytes' overflow
test gains the avail >= maxread leg (Hare's pending >= readahead
predicate) so a growable scanner refills instead of overflowing.
finish ports the free(scan.buffer) verbatim per the regex #27
precedent. Tests: rune scan over 1/2/3/4-byte UTF-8 + EOF,
invalid initial/truncated/surrogate sequences, newscanner grow
round-trip + scanrune-over-newscanner, maxread overflow.
Hojun-Cho
b7a4eda40a