Reinstating the batch HasError property (#214)

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/Contracts/BatchSummary.cs

@@ -25,6 +25,11 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
         /// </summary>
         public string ExecutionStart { get; set; }
 
+        /// <summary>
+        /// Whether or not the batch encountered an error that halted execution
+        /// </summary>
+        public bool HasError { get; set; }
+
         /// <summary>
         /// The ID of the result set within the query results
         /// </summary>