public byte[] hashFull(String s) {
        return digester.digest(Utf8.toBytes(s));
    }
Convenience class for hashing a String with MD5, and either returning
an int with the 4 LSBytes, or the whole 12-byte MD5 hash.
<p>
Note that instantiating this class can be expensive, so re-using instances
is a good idea.
<p>
This class is not thread safe.

@author Einar M R Rosenvinge
vespajlib/src/main/java/com/yahoo/collections/MD5.java