pgsql: Fix json_to_record() bug with nested objects.

Fix json_to_record() bug with nested objects.

A thinko concerning nesting depth caused json_to_record() to produce bogus
output if a field of its input object contained a sub-object with a field
name matching one of the requested output column names.  Per bug #13996
from Johann Visagie.

I added a regression test case based on his example, plus parallel tests
for json_to_recordset, jsonb_to_record, jsonb_to_recordset.  The latter
three do not exhibit the same bug (which suggests that we may be missing
some opportunities to share code...) but testing seems like a good idea
in any case.

Back-patch to 9.4 where these functions were introduced.

Branch
------
REL9_5_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/429d6846572fe43dc11496adfeaecadf23925e3f

Modified Files
--------------
src/backend/utils/adt/jsonfuncs.c   |  2 +-
src/test/regress/expected/json.out  | 16 ++++++++++++++++
src/test/regress/expected/jsonb.out | 16 ++++++++++++++++
src/test/regress/sql/json.sql       |  7 +++++++
src/test/regress/sql/jsonb.sql      |  8 ++++++++
5 files changed, 48 insertions(+), 1 deletion(-)