pgsql: Add array_to_json and row_to_json functions.

Add array_to_json and row_to_json functions.

Also move the escape_json function from explain.c to json.c where it
seems to belong.

Andrew Dunstan, Reviewd by Abhijit Menon-Sen.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/39909d1d39ae57c3a655fc7010e394e26b90fec9

Modified Files
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doc/src/sgml/func.sgml | 59 ++++++
src/backend/commands/explain.c | 47 +-----
src/backend/utils/adt/json.c | 354 +++++++++++++++++++++++++++++++++++-
src/include/catalog/pg_proc.h | 8 +
src/include/utils/json.h | 5 +
src/test/regress/expected/json.out | 111 +++++++++++
src/test/regress/sql/json.sql | 43 +++++
7 files changed, 579 insertions(+), 48 deletions(-)