pgsql: Correct volatility markings of a few json functions.

Correct volatility markings of a few json functions.

json_agg and json_object_agg and their associated transition functions
should have been marked as stable rather than immutable, as they call IO
functions indirectly. Changing this probably isn't going to make much
difference, as you can't use an aggregate function in an index
expression, but we should be correct nevertheless.

json_object, on the other hand, should be marked immutable rather than
stable, as it does not call IO functions.

As discussed on -hackers, this change is being made without bumping the
catalog version, as we don't want to do that at this stage of the cycle,
and the changes are very unlikely to affect anyone.

Branch
------
REL9_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/6e0a053a963024698de8ba315eed7455520d1a92

Modified Files
--------------
src/include/catalog/pg_proc.h | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)