Fix Informix Boolean Type

Fixes #1016

Author: hazzik

src/NHibernate.Test/DialectTest/InformixDialectFixture.cs

@@ -0,0 +1,24 @@
+using NHibernate.Dialect;
+using NHibernate.SqlCommand;
+using NUnit.Framework;
+
+namespace NHibernate.Test.DialectTest
+{
+	[TestFixture]
+	public class InformixDialectFixture
+	{
+		private readonly InformixDialect _dialect = new InformixDialect();
+
+		[Test]
+		public void ToBooleanValueStringTrue()
+		{
+			Assert.That(_dialect.ToBooleanValueString(true), Is.EqualTo("'t'"));
+		}
+
+		[Test]
+		public void ToBooleanValueStringFalse()
+		{
+			Assert.That(_dialect.ToBooleanValueString(false), Is.EqualTo("'f'"));
+		}
+	}
+}

src/NHibernate/Dialect/InformixDialect.cs

@@ -337,7 +337,7 @@ public override JoinFragment CreateOuterJoinFragment()
 		/// <returns> The appropriate SQL literal. </returns>
 		public override string ToBooleanValueString(bool value)
 		{
-			return value ? "t" : "f";
+			return value ? "'t'" : "'f'";
 		}
 
 		/// <summary>