Add missing files

src/aeso_utils.hrl

@@ -0,0 +1,6 @@
+-define(IS_CONTRACT_HEAD(X),
+        (X =:= contract_main orelse
+         X =:= contract_interface orelse
+         X =:= contract_child
+        )
+       ).

test/contracts/interface_with_defs.aes

@@ -0,0 +1,5 @@
+contract interface ContractOne =
+  entrypoint foo() = "foo"
+
+contract ContractTwo =
+  entrypoint bar() = "bar"