fts returning same subjects for Relevancy queries

I'd be nice to add a new ResultType for FTS - SUBJECT_RELEVANCY.

A little talk on IRC:
<mhr3> kamstrup, it's a bit weird that when using ResultType.RELEVANCY, the same subjects get returned multiple times
<kamstrup> mhr3: that'll be hard to "fix" when you think about it it's really the right thing we do imho
 mhr3: it's relevancy ordered search over the events
<kamstrup> not the subjects
<mhr3> kamstrup, otoh most of the data that gets indexed comes from the subject
<kamstrup> mhr3: perhaps you want a a ResultType.SUBJECTS_BY_RELEVANCY
<mhr3> yea, i guess i do
<kamstrup> mhr3: i agree with the general idea that clustering on subject would be nice