pgsql: PL/Python: Make tests pass with Python 3.5

PL/Python: Make tests pass with Python 3.5

The error message wording for AttributeError has changed in Python 3.5.
For the plpython_error test, add a new expected file.  In the
plpython_subtransaction test, we didn't really care what the exception
is, only that it is something coming from Python.  So use a generic
exception instead, which has a message that doesn't vary across
versions.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f16d52269a196f7f303abe3b978d95ade265f05f

Modified Files
--------------
src/pl/plpython/expected/README                    |    1 +
src/pl/plpython/expected/plpython_error_5.out      |  428 ++++++++++++++++++++
.../plpython/expected/plpython_subtransaction.out  |   12 +-
.../expected/plpython_subtransaction_0.out         |    8 +-
.../expected/plpython_subtransaction_5.out         |    8 +-
src/pl/plpython/sql/plpython_subtransaction.sql    |    4 +-
6 files changed, 445 insertions(+), 16 deletions(-)