do TEST2 only if TEST1 was positive

[jidanni]

Sure we can do
  meta META0 TEST1 && TEST2
but say TEST2 is expensive, and we only want it to be run if TEST1 is
positive. I suppose SpamAssassin's whole train of thought has no ifs
ands or buts, other than a method of quitting early, but that not what
I want to do. I suppose branching is only possible on the procmail level.