Python 2.5 vs the buildfarm

I notice that we now have four buildfarm members failing in the 8.1
branch, with symptoms indicating that they are running python 2.5,
which pre-8.2 plpython has known incompatibilities with.  I think
it's high time we back-patched those compatibility fixes ... they've
been in the field long enough in 8.2 and 8.3 that the argument that they
pose a breakage risk seems pretty weak.  Comments?

(BTW, the only reason 8.0 and 7.4 aren't failing likewise is that
there's no automated regression test for the PLs in those branches.)
        regards, tom lane