Add a strong mode implementation of LUB to fasta; use it to infer ?:

pkg/front_end/test/fasta/compile.status

Index: pkg/front_end/test/fasta/compile.status
diff --git a/pkg/front_end/test/fasta/compile.status b/pkg/front_end/test/fasta/compile.status
index 2472fe1bf0be5ad13dcd6edfeef5f89d6fbc693c..13bab063c1d94bb8bd3bcc5f50b1156bb7e48f73 100644
--- a/pkg/front_end/test/fasta/compile.status
+++ b/pkg/front_end/test/fasta/compile.status
@@ -26,6 +26,7 @@ uninitialized_fields: Fail # Missing types and unnecessary default values.
 void-methods: Fail # Bad return from setters.
 
 inference/*: Fail
+inference/conditional_lub: Pass

[ahe, 2017/05/02 18:32:56]

I think this test is now marked flaky. You probably need to list all the tests
except conditional_lub.

[Paul Berry, 2017/05/03 17:31:25]

Thanks.  Konstantin took care of this in a CL that landed before mine.

 inference/int_upwards_local: Pass
 inference/local_constructor_from_arguments: Pass
 inference/local_reference_upwards_local: Pass