added ignore_unmapped support to SortDescriptor

Author: Mpdreamz

src/Nest.Tests.Unit/Search/Sort/SortTests.cs

@@ -17,6 +17,7 @@ public void TestSort()
 					.OnField(e => e.Country)
 					.MissingLast()
 					.Descending()
+					.IgnoreUnmappedFields(true)
 				);
 			var json = TestElasticClient.Serialize(s);
 			var expected = @"
@@ -26,7 +27,8 @@ public void TestSort()
                   sort: {
                     country: {
                       missing: ""_last"",
-                      order: ""desc""
+                      order: ""desc"",
+					  ignore_unmapped: true
                     }
                   }
                 }";

src/Nest/DSL/SortDescriptor.cs

@@ -23,6 +23,9 @@ public class SortDescriptor<T> where T : class
 
     [JsonProperty("nested_path")]
     internal string _NestedPath { get; set; }
+	
+	[JsonProperty("ignore_unmapped")]
+	internal bool? _IgnoreUnmappedFields { get; set; }
 
     public virtual SortDescriptor<T> OnField(string field)
     {
@@ -60,6 +63,11 @@ public virtual SortDescriptor<T> MissingValue(string value)
       this._Missing = value;
       return this;
     }
+	public virtual SortDescriptor<T> IgnoreUnmappedFields(bool ignore = true)
+	{
+		this._IgnoreUnmappedFields = ignore;
+		return this;
+	}
     public virtual SortDescriptor<T> Ascending()
     {
       this._Order = "asc";