NH-2176 - on session disposal, release connection as soon as possible.

Author: fredericDelaporte

src/NHibernate/AdoNet/ConnectionManager.cs

@@ -383,6 +383,12 @@ public void EnlistIfRequired()
 		private bool RequireConnectionSwapInDtc
 			=> _ownConnection && Factory.Dialect.SupportsConcurrentWritingConnectionsInSameTransaction;
 
+		public void ReleaseConnectionIfUneededForDtc()
+		{
+			if (RequireConnectionSwapInDtc)
+				DisconnectOwnConnection();
+		}
+
 		public IDisposable FlushingFromDtcTransaction
 		{
 			get

src/NHibernate/Transaction/AdoNetWithDistributedTransactionFactory.cs

@@ -73,8 +73,19 @@ public void ExecuteWorkInIsolation(ISessionImplementor session, IIsolatedWork wo
 		public class DistributedTransactionContext : ITransactionContext, IEnlistmentNotification
 		{
 			public System.Transactions.Transaction AmbientTransation { get; set; }
-			public bool ShouldCloseSessionOnDistributedTransactionCompleted { get; set; }
 
+			public bool ShouldCloseSessionOnDistributedTransactionCompleted
+			{
+				get { return _shouldCloseSessionOnDistributedTransactionCompleted; }
+				set
+				{
+					_shouldCloseSessionOnDistributedTransactionCompleted = value;
+					if (value)
+						_sessionImplementor.ConnectionManager.ReleaseConnectionIfUneededForDtc();
+				}
+			}
+
+			private bool _shouldCloseSessionOnDistributedTransactionCompleted;
 			private readonly ISessionImplementor _sessionImplementor;
 			private readonly ManualResetEvent _waitEvent = new ManualResetEvent(true);
 			private readonly AsyncLocal<bool> _bypassWait = new AsyncLocal<bool>();