Improved error messages about unsupported relations

Author: mac-cain13

CoreDataKit/Importing/NSManagedObject+Importing.swift

@@ -198,11 +198,11 @@ extension NSManagedObject
             }
 
         case let .Some(value as [AnyObject]):
-            let error = NSError(domain: CoreDataKitErrorDomain, code: CoreDataKitErrorCode.UnimplementedMethod.rawValue, userInfo: [NSLocalizedDescriptionKey: "Multiple referenced / nested relationships not yet supported with relation type \(RelationType.Embedding)"])
+            let error = NSError(domain: CoreDataKitErrorDomain, code: CoreDataKitErrorCode.UnimplementedMethod.rawValue, userInfo: [NSLocalizedDescriptionKey: "Multiple nested relationships not yet supported with relation type \(RelationType.Embedding)"])
             return Result(error)
 
         case let .Some(value):
-            let error = NSError(domain: CoreDataKitErrorDomain, code: CoreDataKitErrorCode.UnimplementedMethod.rawValue, userInfo: [NSLocalizedDescriptionKey: "Referenced relationships not yet supported with relation type \(RelationType.Embedding)"])
+            let error = NSError(domain: CoreDataKitErrorDomain, code: CoreDataKitErrorCode.UnimplementedMethod.rawValue, userInfo: [NSLocalizedDescriptionKey: "Referenced relationships are not supported with relation type \(RelationType.Embedding)"])
             return Result(error)
 
         case .Null: