more on term_year_series_frame()
fixes for tm_yearly_totals_meta

FIXME: some code duplication in the various functions that produce and
plot yearly series; some inconsistency in the handling of the parameters
for these
corpus_dist_plot

For seeing a mallet diagnostic. cf.
cc.mallet.topics.TopicModelDiagnostics.getDistanceFromCorpus() for the
calculation.

also: correct ignored parameter in topic_names()