pgsql: Code review for error reports in jsonb_set().

Code review for error reports in jsonb_set().

User-facing (even tested by regression tests) error conditions were thrown
with elog(), hence had wrong SQLSTATE and were untranslatable.  And the
error message texts weren't up to project style, either.

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1548c781888be14d2f24d65fbd591198fabef3a0

Modified Files
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src/backend/utils/adt/jsonfuncs.c   | 24 ++++++++++++++----------
src/test/regress/expected/jsonb.out | 12 ++++++------
2 files changed, 20 insertions(+), 16 deletions(-)