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.
Back-patch of commit f16d52269a, which
was previously back-patched into 9.2-9.4, but missed 9.5.
