Minimum supported version of Python?

Our documentation claims that the minimum Python version for plpython
is 2.3. However, an attempt to build with that on an old Mac yielded
a bunch of failures in the plpython_types regression test, all of the
form

! ERROR: could not import a module for Decimal constructor
! DETAIL: ImportError: No module named decimal

A quick trawl through the buildfarm revealed no evidence that we're
actually testing anything older than Python 2.5, which is why this
wasn't evident awhile ago. It looks like the failing test cases
date back to PG 9.0.

Personally I have no desire to put any effort into fixing this, and
thus suggest that we just change the documentation to specify that 2.5
is the minimum Python version since 9.0. Does anybody else want to
work harder on it, and if so what would you propose doing exactly?

regards, tom lane