Levenshtein distance problem

```
According to API docs, the Levenshtein distance is at most equal to the length
of the longer string. This seems not to be the case.

What steps will reproduce the problem?
1. use the following code

from diff_match_patch import diff_match_patch
s1 = u'My creative work'
s2 = u'Adding another item'
differ = diff_match_patch()
diffs = differ.diff_main(s1, s2)

print differ.diff_levenshtein(diffs)
print max([s1, s2])

print differ.diff_levenshtein(diffs)
print [len(s1), len(s2)]

What is the expected output? What do you see instead?
should be 16, but 21 (?!) is produced

What version of the product are you using? On what operating system?
diff-match-patch==20121119

Please provide any additional information below.
...or do I get the APIwrong?

```

Original issue reported on code.google.com by `adrian.b...@wilabs.com` on 27 Oct 2014 at 3:41