pgsql: Fix jsonb replace and delete on scalars and empty structures

Fix jsonb replace and delete on scalars and empty structures

These operations now error out if attempted on scalars, and simply
return the input if attempted on empty arrays or objects. Along the way
we remove the unnecessary cloning of the input when it's known to be
unchanged. Regression tests covering these cases are added.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/3f2cec797ecceb7467e365410506c0817f9d0163

Modified Files
--------------
src/backend/utils/adt/jsonfuncs.c     |   88 +++++++++++++--------------------
src/test/regress/expected/jsonb.out   |   57 +++++++++++++++++++++
src/test/regress/expected/jsonb_1.out |   57 +++++++++++++++++++++
src/test/regress/sql/jsonb.sql        |   16 ++++++
4 files changed, 165 insertions(+), 53 deletions(-)