If a checksum word is present, language detection would use
just the word prefixes. However, a set of word prefixes may
be found in more than one language, and so the wrong language
may be found first, which could then fail the checksum, since
the check may be done with a different unique prefix length
from the one it was created from.
We now make a checksum test when we we detect a language from
prefixes only, to make sure we have the correct one.
Some word triplets, such as "mugged names nail", are not valid
results from any 32 bit value. If used to decode a 32 bit value,
the result will therefore encode to a different word triplet.
Fix this by using random words converted from an actual random
bitstring, ensuring we always get valid triplets.
