moving aggregate bad error message

I was wondering if I could just add minvfunc, and have the rest of the m*
functions be assumed to be the same as their non-moving counterparts.
Apparently the answer is 'no'. But in the process, I found a bad error
message. When omitting mfinalfunc when there is a finalfunc, I get the
error:

"ERROR: moving-aggregate implementation returns type jj_state, but plain
implementation returns type jj_state." A rather peculiar
complaint, analogous to the infamous "something failed: Success".

Looking at the code, it seems we are testing rettype != finaltype, but
reporting aggmTransType and aggTransType. Why aren't we reporting what we
are testing?

With the attached patch, it gives the more sensible "ERROR:
moving-aggregate implementation returns type jj_state, but plain
implementation returns type numeric."

Cheers,

Jeff