Compare two arrays in "length-constant" time. This thwarts timing-based
attacks by guaranteeing all comparisons (of
a given length) take the same
amount of time.
See the section "Why does the hashing code on this page compare the hashes in "length-constant" time?" at: https://crackstation.net/hashing-security.htm
bool lengthConstantEquals( ubyte a, ubyte b );