SearchIdx.pm: Make indexing search positions optional
About half the size of the Xapian search index turns out to be search
positions. The search positions are only used in a very narrow set of
queries. Make the search positions optional so people don't need to
pay the cost of queries they will never make.
This also makes public-inbox more approachable for light hacking as
generating all of the indexes is time consuming.
The way this is done is to add a method to SearchIdx called index_text
that wraps the call of the term generator method index_text. The new
index_text method takes care of calling both index_text and
increase_termpos (the two functions that are responsible for position
data).
Then index_users, index_diff_inc, index_old_diff_fn, index_diff,
index_body are made proper methods that calls the new index_text.
Callers of the new index_text are slightly simplified as they don't
need to call increase_termpos as well.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>