Crash with PostgreSQL 7.4

[Peter Eisentraut]

Fernando Nasser wrote:
> I wonder if this is not already in the rdhb-explain cvs tip. 
> Originally RHDB-3-0 was a 7.3.x release and I may have avoided
> changing the branch.

AFAICT, the code in the head and in the RHDB-3-0 branch is all the same.  
Also, the RHDB-3-0 code does contain a comment that it was modified for 
7.4, so I figured it was a plain oversight.