pgsql: plpython: Add SPI cursor support

plpython: Add SPI cursor support

Add a function plpy.cursor that is similar to plpy.execute but uses an
SPI cursor to avoid fetching the entire result set into memory.

Jan Urbański, reviewed by Steve Singer

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/89e850e6fda9e4e441712012abe971fe938d595a

Modified Files
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doc/src/sgml/plpython.sgml | 81 +++
src/pl/plpython/expected/plpython_spi.out | 151 +++++
.../plpython/expected/plpython_subtransaction.out | 66 ++
.../expected/plpython_subtransaction_0.out | 70 +++
.../expected/plpython_subtransaction_5.out | 70 +++
src/pl/plpython/expected/plpython_test.out | 6 +-
src/pl/plpython/plpython.c | 642 ++++++++++++++++++++
src/pl/plpython/sql/plpython_spi.sql | 116 ++++
src/pl/plpython/sql/plpython_subtransaction.sql | 52 ++
9 files changed, 1251 insertions(+), 3 deletions(-)