Back-patch plpgsql fix for rowtypes with dropped columns?

I'm getting some pressure at Red Hat to back-patch this fix:
http://archives.postgresql.org/pgsql-committers/2009-08/msg00068.php
(commit dcb2bda9b7042dbf43f876c94ebf35d951de10e9)
into the RHEL 8.4.x postgresql release. Since I have to do the work
anyway, it seems to me to be sensible to commit the fix into community
git as well, so that it will be available to everybody in future 8.4.x
releases. 9.0 has now been out long enough that there seems no real
risk of introducing new bugs, which was the reason for not back-patching
at the time.

The original patch modified execQual.c and some executor runtime structs
to make use of the new tupconvert.c file. I'm a bit inclined to reduce
the footprint of the back-patch by not touching execQual.c, but just
allowing there to be some duplicated code. That would avoid any risk
of breaking third-party code that might be looking at struct
ConvertRowtypeExprState.

I don't currently have a need to fix this before 8.4, and it looks like
the existing patch doesn't apply easily to 8.3 anyway. So I'm only
proposing to do this in 8.4.

Comments, objections?

regards, tom lane