pgsql: Unpack jbvBinary objects passed to pushJsonbValue

Unpack jbvBinary objects passed to pushJsonbValue

pushJsonbValue was accepting jbvBinary objects passed as WJB_ELEM or
WJB_VALUE data. While this succeeded, when those objects were later
encountered in attempting to convert the result to Jsonb, errors
occurred. With this change we ghuarantee that a JSonbValue constructed
from calls to pushJsonbValue does not contain any jbvBinary objects.
This cures a problem observed with jsonb_delete.

This means callers of pushJsonbValue no longer need to perform this
unpacking themselves. A subsequent patch will perform some cleanup in
that area.

The error was not triggered by any 9.4 code, but this is a publicly
visible routine, and so the error could be exercised by third party
code, therefore backpatch to 9.4.

Bug report from Peter Geoghegan, fix by me.

Branch
------
REL9_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/9b74f32cdbff8b9be47fc69164eae552050509ff

Modified Files
--------------
src/backend/utils/adt/jsonb_util.c | 44 ++++++++++++++++++++++++++++++++----
src/include/utils/jsonb.h | 2 +-
2 files changed, 40 insertions(+), 6 deletions(-)