Fixed bug in json_to_xliff._insert_breaks() and added tests.
Specifically, this failed to add back periods at ends of sentences.

R=neil.fraser@gmail.com

Review URL: https://codereview.appspot.com/9835043

git-svn-id: http://blockly.googlecode.com/svn/trunk@1016 c400ca83-b69d-9dd7-9705-49c6b8615e23