Refine definition of what it is to be a vacuous pattern

Now, the code no longer classifies

  ([], []) => []

as vacuous.

src/boss/theory_tests/onelineScript.sml

@@ -140,6 +140,6 @@ Definition test_def:
 End
 
 Theorem oneline_test[local] = DefnBase.one_line_ify NONE test_def
-
+val _ = assert is_oneline oneline_test
 
 val _ = export_theory();

src/coretypes/DefnBase.sml

@@ -468,8 +468,10 @@ fun one_line_ify heuristic def =
             let
               fun test ((_, args), bod) =
                   let val pat = List.nth(args, cnum)
+                      val (_, args_of) = strip_comb pat
                   in
                     not (is_var pat) andalso
+                    List.all is_var args_of andalso
                     null (op_intersect aconv (free_vars bod) (free_vars pat))
                   end
             in