Correct implementation of joaat hash.

[kohler]

Before this commit, the result produced by a joaat hash depended
on how the input data was chunked. A hash produced by multiple
hash_update operations was incorrect. For example, this code,
which should produce three identical lines:

var_dump(hash("joaat", "abcd"));

$hash = hash_init("joaat");
hash_update($hash, "ab");
hash_update($hash, "cd");
var_dump(hash_final($hash));

$hash = hash_init("joaat");
hash_update($hash, "abc");
hash_update($hash, "d");
var_dump(hash_final($hash));

instead produced:

string(8) "cd8b6206"
string(8) "e590d137"
string(8) "2d59d087"

This is because the finalization step, involving shift operations
and adds, was applied on every chunk, rather than once at the end
as is required by the hash definition.

After this commit, the code above produces:

string(8) "cd8b6206"
string(8) "cd8b6206"
string(8) "cd8b6206"

as expected.

Some tests encoded the wrong behavior and were corrected.