pgsql: PL/Python: Improve Python 3 regression test setup

PL/Python: Improve Python 3 regression test setup

Currently, we are making mangled copies of plpython/{expected,sql} to
plpython/python3/{expected,sql}, and run the tests in
plpython/python3. This has the disadvantage that the regression.diffs
file, if any, ends up in plpython/python3, which is not the normal
location. If we instead make the mangled copies in
plpython/{expected,sql}/python3/, we can run the tests from the normal
directory, regression.diffs ends up the normal place, and the
pg_regress invocation also becomes a lot simpler. It's also more
obvious at run time what's going on, because the tests end up being
named "python3/something" in the test output.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b2e3bea3afe9618764a8f15cc7d6d95036b7638b

Modified Files
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src/pl/plpython/.gitignore | 2 ++
src/pl/plpython/Makefile | 35 ++++++++++++++++++++++-------------
2 files changed, 24 insertions(+), 13 deletions(-)