Pbkdf2 hashers should accept variable checksum sizes
Created originally on Bitbucket by Anonymous
The pbkdf2_* hashers currently have a fixed checksum size -- that of the underlying digest.
In order to allow them to handle hashes converted from other sources (which e.g. have 16 byte digests, even for sha256), this should be changed so .hash() uses checksum_size as the default, but .verify() adapts the size to whatever the input hash uses.