pgsql: Improve support for composite types in PL/Python.

Improve support for composite types in PL/Python.

Allow PL/Python functions to return arrays of composite types.
Also, fix the restriction that plpy.prepare/plpy.execute couldn't
handle query parameters or result columns of composite types.

In passing, adopt a saner arrangement for where to release the
tupledesc reference counts acquired via lookup_rowtype_tupdesc.
The callers of PLyObject_ToCompositeDatum were doing the lookups,
but then the releases happened somewhere down inside subroutines
of PLyObject_ToCompositeDatum, which is bizarre and bug-prone.
Instead release in the same function that acquires the refcount.

Ed Behn and Ronan Dunklau, reviewed by Abhijit Menon-Sen

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8b6010b8350a1756cd85595705971df81b5ffc07

Modified Files
--------------
doc/src/sgml/plpython.sgml                      |    7 -----
src/pl/plpython/expected/plpython_composite.out |   12 +++++---
src/pl/plpython/expected/plpython_spi.out       |   15 ++++++++++
src/pl/plpython/expected/plpython_types.out     |   13 ++++-----
src/pl/plpython/expected/plpython_types_3.out   |   13 ++++-----
src/pl/plpython/plpy_exec.c                     |    2 ++
src/pl/plpython/plpy_spi.c                      |    7 +----
src/pl/plpython/plpy_typeio.c                   |   35 ++++++++++++-----------
src/pl/plpython/sql/plpython_composite.sql      |    2 +-
src/pl/plpython/sql/plpython_spi.sql            |   12 ++++++++
src/pl/plpython/sql/plpython_types.sql          |    2 +-
11 files changed, 70 insertions(+), 50 deletions(-)