Dave,
To clarify my reasoning for exposing the patch, Lee Denison had committed this to HEAD earlier (with a few other changes, like ... eq ... replacing [string equal ... ...]). What I did was take his patch and remove everything but the one thing that did the job.
If I understand correctly, feature adds to 5.2 are frozen. My intent was not to change 5.2 as shipped, but rather to provide folks running 5.2 with a working callback functionality if they personally wanted it; if so, they would apply the patch and restart their server.
To clarify what the patch does, it can be seen by looking at the patch itself: the else clause of that structure causes an argument parser to be built. The change adds an additional condition which must be satisfied to -not- build an argument parser: the ad_proc must not be defining a callback.
