amcheck/verify_heapam doesn't check for interrupts

I just noticed that the new heapam amcheck verification code can take
a very long time to respond to cancellations from pg_amcheck -- I saw
that it took over 2 minutes on a large database on my workstation.

It looks like we neglect to call CHECK_FOR_INTERRUPTS() anywhere
inside verify_heapam.c. Is there any reason for this? Can't we just
put a CHECK_FOR_INTERRUPTS() at the top of the outermost loop, inside
verify_heapam()?

Not sure if pg_amcheck itself is a factor here too -- didn't get that far.

Thanks
-- 
Peter Geoghegan