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
--------------
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(-)