ts_count

One of our PostgreSQL Experts Inc customers wanted a function to count
all the occurrences of terms in a tsquery in a tsvector. This has been
written as a loadable module function, and initial testing shows it is
working well. With the client's permission we are releasing the code -
it's available at <https://github.com/pgexperts/ts_count>. The actual
new code involved here is tiny, some of the code is C&P'd from tsrank.c
and much of the rest is boilerplate.

A snippet from the regression test:

select ts_count(to_tsvector('managing managers manage peons
managerially'),
to_tsquery('managers | peon'));
ts_count
----------
4

We'd like to add something like this for 9.2, so I'd like to get the API agreed and then I'll prepare a patch and submit it for the next CF.

Comments? cheers andrew