fix #1880 by using a simple trick to fix widow words

fix #1880 by using a simple trick to fix widow words
Before:
![screen shot 2014-11-03 at 17 47 45](https://cloud.githubusercontent.com/assets/40213/4886082/570a7f70-6379-11e4-8093-6199871e8748.png)


After:
![screen shot 2014-11-03 at 14 59 44](https://cloud.githubusercontent.com/assets/40213/4886081/549ef93c-6379-11e4-95a7-66e14995b84a.png)
It should, but when the replaced character is inside a span, that doesn't work. Example: 
`This is a <b>beautiful pony</b>` would be transformed to 
`This is a beautiful[non breaking space]<b>pony</b>` with `TextUtils.concat` only.