dos2unix: convert stop-words

*   Remove `'` characters as they are filtered already.
Remove only whole words in stop-word filter

We were removing wholes _and_ substrings of other words which causes
problems later down the pipeline. By adding word boundaries to the pattern,
we remove only the whole word any where in the text.

[1]: http://stackoverflow.com/questions/9308072/remove-whole-word-only-with-java