pgsql: PL/Python: Convert numeric to Decimal

PL/Python: Convert numeric to Decimal

The old implementation converted PostgreSQL numeric to Python float,
which was always considered a shortcoming. Now numeric is converted to
the Python Decimal object. Either the external cdecimal module or the
standard library decimal module are supported.

From: Szymon Guz <mabewlun(at)gmail(dot)com>
From: Ronan Dunklau <rdunklau(at)gmail(dot)com>
Reviewed-by: Steve Singer <steve(at)ssinger(dot)info>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7919398bac8bacd75ec5d763ce8b15ffaaa3e071

Modified Files
--------------
doc/src/sgml/plpython.sgml | 23 +++++++++---
src/pl/plpython/expected/plpython_types.out | 49 +++++++++++++++++++++----
src/pl/plpython/expected/plpython_types_3.out | 49 +++++++++++++++++++++----
src/pl/plpython/plpy_typeio.c | 42 ++++++++++++++++-----
src/pl/plpython/sql/plpython_types.sql | 9 ++++-
5 files changed, 138 insertions(+), 34 deletions(-)