pgsql: PL/Python: Improve test coverage

PL/Python: Improve test coverage

Add test cases for inline handler of plython2u (when using that
language name), and for result object element assignment.  There is
now at least one test case for every top-level functionality, except
plpy.Fatal (annoying to use in regression tests) and result object
slice retrieval and slice assignment (which are somewhat broken).

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/e6c2e8cb87846161033e1f215876c4b95f631df0

Modified Files
--------------
src/pl/plpython/expected/plpython_do.out  |    3 +++
src/pl/plpython/expected/plpython_spi.out |   20 ++++++++++++++++++++
src/pl/plpython/sql/plpython_do.sql       |    2 ++
src/pl/plpython/sql/plpython_spi.sql      |   15 +++++++++++++++
4 files changed, 40 insertions(+), 0 deletions(-)