Don't break the world if enum in annotation isn't found

compiler/frontend/src/org/jetbrains/jet/lang/resolve/constants/ErrorValue.java

@@ -50,4 +50,9 @@ public class ErrorValue implements CompileTimeConstant<Void> {
     public String getMessage() {
         return message;
     }
+
+    @Override
+    public String toString() {
+        return message;
+    }
 }

compiler/frontend/src/org/jetbrains/jet/lang/types/ErrorUtils.java

@@ -385,7 +385,8 @@ public class ErrorUtils {
         return createErrorType(value + " is not allowed here", value.getType().getMemberScope());
     }
 
-    public static ClassifierDescriptor getErrorClass() {
+    @NotNull
+    public static ClassDescriptor getErrorClass() {
         return ERROR_CLASS;
     }