examples: lang: Test that each of the mcl examples compiles

We let these rot, so fixup the issues and test them!

examples/lang/sendrecv1.mcl

@@ -13,7 +13,7 @@ exec "exec0" {
 kv "kv0" {
 	key => $ns,
 	#value => "two",
-	mapped = true,
+	#mapped => true,
 }
 
 Exec["exec0"].output -> Kv["kv0"].value