Revert to more specific handling of situation

Convert.ToString might cover bugs from unintentional usage of other data types and is culture specific

Author: csharper2010

src/NHibernate/Type/AbstractStringType.cs

@@ -57,15 +57,17 @@ public AbstractStringType(SqlType sqlType)
 		public override void Set(DbCommand cmd, object value, int index, ISessionImplementor session)
 		{
 			var parameter = cmd.Parameters[index];
-			var stringValue  = Convert.ToString(value);
+
+			if (value is Enum)
+				value = Enum.GetName(value.GetType(), value);
 
 			//Allow the driver to adjust the parameter for the value
-			session.Factory.ConnectionProvider.Driver.AdjustParameterForValue(parameter, SqlType, stringValue);
+			session.Factory.ConnectionProvider.Driver.AdjustParameterForValue(parameter, SqlType, value);
 
 			// set the parameter value before the size check, since ODBC changes the size automatically
-			parameter.Value = stringValue;
+			parameter.Value = value;
 
-			if (parameter.Size > 0 && stringValue.Length > parameter.Size)
+			if (parameter.Size > 0 && value != null && ((string) value).Length > parameter.Size)
 				throw new HibernateException("The length of the string value exceeds the length configured in the mapping/parameter.");
 		}