Fixed: Validate if equals or child for startup folder

Fixes #1712
Close #1713

(cherry picked from commit 0991cfe27efd6ddb533227b25754661e18d7e9ad)

src/NzbDrone.Core/Validation/Paths/StartupFolderValidator.cs

@@ -9,7 +9,7 @@ namespace NzbDrone.Core.Validation.Paths
         private readonly IAppFolderInfo _appFolderInfo;
 
         public StartupFolderValidator(IAppFolderInfo appFolderInfo)
-            : base("Path cannot be an ancestor of the start up folder")
+            : base("Path cannot be {relationship} the start up folder")
         {
             _appFolderInfo = appFolderInfo;
         }
@@ -21,7 +21,24 @@ namespace NzbDrone.Core.Validation.Paths
                 return true;
             }
 
-            return !_appFolderInfo.StartUpFolder.IsParentPath(context.PropertyValue.ToString());
+            var startupFolder = _appFolderInfo.StartUpFolder;
+            var folder = context.PropertyValue.ToString();
+
+            if (startupFolder.PathEquals(folder))
+            {
+                context.MessageFormatter.AppendArgument("relationship", "set to");
+
+                return false;
+            }
+
+            if (startupFolder.IsParentPath(folder))
+            {
+                context.MessageFormatter.AppendArgument("relationship", "child of");
+
+                return false;
+            }
+
+            return true;
         }
     }
 }