Python 3.x versus PG 9.1 branch

In view of our rather embarrassing failure to cover the back branches
with Python 3.5-related regression test adjustments, I think there is
a clear need for a buildfarm critter that's testing with Python 3.5,
and I've been working on setting one up. It's passing at the moment
for 9.2 and up, but not for 9.1, because we've repeatedly not bothered
to back-port regression test fixes for newer Pythons into that branch.
I could just omit Python 3 coverage for that branch in the critter's
configuration, but I wonder exactly why things are that way.

For clarity, to cover 9.1 I think we'd need to back-patch some subset
of these commits:

f16d52269 ff2faeec5 d0765d50f 6bff0e7d9 527ea6684 8182ffde5
45d1f1e02 2cfb1c6f7

The precedent of not fixing 9.1 started with the last of these.

I haven't looked into the details of which changes would actually
apply to 9.1, I just searched for commits that touched the Python
regression tests. We'd really only need enough changes to address
the regression failures I'm getting, which are attached below.

Or we could just blow it off on the grounds that 9.1 is not long
for this world anyhow.

Opinions anyone?

regards, tom lane