Rename compare_values, hash_values with "_short" suffix.

Rename compare_values, hash_values with "_short" suffix.

The compare_values and hash_values functions do not compare an
entire value.  Rather, they compare only the short string prefix
of long string values.  I have a feeling that this misnaming was
confusing people (it certainly confused me) so this commit renames
them.

It also adds a new function value_compare_3way() that does what
one what expect such a function to do.