pgsql: Fix ts_delete(tsvector, text[]) to cope with duplicate array ent

Fix ts_delete(tsvector, text[]) to cope with duplicate array entries.

Such cases either failed an Assert, or produced a corrupt tsvector in
non-Assert builds, as reported by Andreas Seltenreich. The reason is
that tsvector_delete_by_indices() just assumed that its input array had
no duplicates. Fix by explicitly de-duping.

In passing, improve some comments, and fix a number of tests for null
values to use ERRCODE_NULL_VALUE_NOT_ALLOWED not
ERRCODE_INVALID_PARAMETER_VALUE.

Discussion: <87invhoj6e(dot)fsf(at)credativ(dot)de>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/c50d192ce33c10fa06411306f8644b4f47ce9a06

Modified Files
--------------
src/backend/utils/adt/tsvector_op.c | 77 +++++++++++++++++++++--------------
src/test/regress/expected/tstypes.out | 6 +++
src/test/regress/sql/tstypes.sql | 1 +
3 files changed, 53 insertions(+), 31 deletions(-)