Javascript version doesn't handle astral code points correctly

[GoogleCodeExporter]

What steps will reproduce the problem?

var dmp = new diffMatchPatch();

var str1 = ">>> \ud83d\ude4b <<<";
var str2 = ">>> \ud83d\ude4c <<<";

var diffs = dmp.diff_main(str1, str2);
console.log("diff = " + JSON.stringify(diffs));

What is the expected output? What do you see instead?

Expected: diff = [[0,">>> "],[-1,"🙋 "],[1,"🙌 "],[0," <<<"]]
Actual: diff = [[0,">>> �"],[-1,"�"],[1,"�"],[0," <<<"]]

Expanded, in case there is a loss of fidelity in this issue posting:

Expected: diff = [[0,">>> "],[-1,"\ud83d\ude4b"],[1,"\ud83d\ude4c"],[0," <<<"]]
Actual: diff = [[0,">>> \ud83d"],[-1,"\ude4b"],[1,"\ude4c"],[0," <<<"]]

The diff is split *between* the surrogate characters of the astral code point. 
Note that str1 and str2 share a common high surrogate.

What version of the product are you using? On what operating system?

1.0.0, on OSX

Please provide any additional information below.

Original issue reported on code.google.com by keit...@rivaliq.com on 1 May 2015 at 2:59