[Pkg-postgresql-public] packaging PL/Python and Python 3

[Peter Eisentraut]

With Python 3 now somewhat supported in Debian, and Python 3 now
somewhat usable in PostgreSQL 9.1, it might be time to put this into a
package.  I'd imagine creating a separate postgresql-plpython3-9.1
package.  That's the easy part.

The hard part: A PostgreSQL build can only support one Python version at
a time.  So to build a plpython2 and a plpython3, we have to pull some
trick, like running a second build in a subdir or something.  I can
think of three or four different ways to approach that, but they're all
pretty ugly.  Anyone got an idea?