Limits of backwards compatibility for psql's \d commands

I'm fooling around with Guillaume Lelarge's patch to make psql's \d
commands work with older server versions. The patch as submitted
works with servers back to 7.4 (modulo a small bug or two). I tried
to see what it'd take to make it work with 7.3. I count about a dozen
trivial diffs and about three nontrivial ones --- nontrivial meaning
I didn't see a simple fix right away. This seems a bit more work than
is justified for a server version that the community has officially
dropped support for, but I wonder if anyone feels hot about it?

Pre-7.3 server versions seem entirely out of the realm of reason because
they lack schema support, meaning all of those "pg_catalog." prefixes
break, not to mention the joins to pg_namespace and the "schema" output
columns. So it's just 7.3 that's worth debating, I think.

regards, tom lane