Override AggregateException.Message to include more detail

ToString() includes details on inner exceptions, but Message does not, with the default message just saying "One or more errors occurred."  This commit overrides Message to append the messages of the inner exceptions as well.

Author: stephentoub

src/mscorlib/src/System/AggregateException.cs

@@ -17,6 +17,7 @@
 using System.Runtime.ExceptionServices;
 using System.Runtime.Serialization;
 using System.Security;
+using System.Text;
 using System.Threading;
 
 namespace System
@@ -431,6 +432,30 @@ public AggregateException Flatten()
             return new AggregateException(Message, flattenedExceptions);
         }
 
+        /// <summary>Gets a message that describes the exception.</summary>
+        public override string Message
+        {
+            get
+            {
+                if (m_innerExceptions.Count == 0)
+                {
+                    return base.Message;
+                }
+
+                StringBuilder sb = StringBuilderCache.Acquire();
+                sb.Append(base.Message);
+                sb.Append(' ');
+                for (int i = 0; i < m_innerExceptions.Count; i++)
+                {
+                    sb.Append('(');
+                    sb.Append(m_innerExceptions[i].Message);
+                    sb.Append(") ");
+                }
+                sb.Length -= 1;
+                return StringBuilderCache.GetStringAndRelease(sb);
+            }
+        }
+
         /// <summary>
         /// Creates and returns a string representation of the current <see cref="AggregateException"/>.
         /// </summary>