pgsql: Fix ts_rank_cd() to ignore stripped lexemes

Fix ts_rank_cd() to ignore stripped lexemes

Previously, stripped lexemes got a default location and could be
considered if mixed with non-stripped lexemes.

BACKWARD INCOMPATIBILITY CHANGE

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/1420f3a9827a39e5c6c998f6fa35a6fc97903145

Modified Files
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doc/src/sgml/textsearch.sgml          |   10 +++++++---
src/backend/utils/adt/tsrank.c        |    5 +++--
src/test/regress/expected/tsearch.out |   14 ++++++++++++++
src/test/regress/sql/tsearch.sql      |    6 ++++++
4 files changed, 30 insertions(+), 5 deletions(-)