pgsql: Reduce json <=> jsonb casts from explicit-only to assignment lev

Reduce json <=> jsonb casts from explicit-only to assignment level.

There's no reason to make users write an explicit cast to store a
json value in a jsonb column or vice versa.

We could probably even make these implicit, but that might open us up
to problems with ambiguous function calls, so for now just do this.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b67f1ce181910e012b3a8ec7a35ba20a48247757

Modified Files
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src/include/catalog/catversion.h |    2 +-
src/include/catalog/pg_cast.h    |    4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)