bugfix: topic_word_scores
bugfix: topic_word_scores

for some mystical reason 'colSums' on a sparseMatrix fails here (but not
when the same code is executed in the main namespace rather than the
package namespace). 'Matrix::colSums' works fine.

joncgoodwin/dfrtopics,joncgoodwin/dfrtopics,agoldst/dfrtopics,agoldst/dfrtopics,agoldst/dfrtopics,agoldst/dfrtopics,joncgoodwin/dfrtopics,agoldst/dfrtopics