Adding IContentQuery.Count() to do a count(*) query

--HG--
branch : dev
extra : transplant_source : %92%FE%95%FEFI%0Co%D6%1D%9A%8Fz%97%18%B2v4%B7%CB

src/Orchard.Tests/ContentManagement/ContentQueryTests.cs

@@ -248,6 +248,15 @@ namespace Orchard.Tests.ContentManagement {
 
         }
 
+        [Test]
+        public void CountReturnsNumber() {
+            AddSampleData();
+
+            var count = _manager.Query()
+                .Count();
+
+            Assert.That(count, Is.EqualTo(4));
+        }
 
         [Test]
         public void QueryShouldJoinVersionedRecords() {

src/Orchard/ContentManagement/DefaultContentQuery.cs

@@ -195,6 +195,11 @@ namespace Orchard.ContentManagement {
                 return _query.Slice(0, 0).AsPart<T>();
             }
 
+            int IContentQuery<T>.Count() {
+                var criteria = _query.BindItemVersionCriteria();
+                return criteria.SetProjection( Projections.RowCount() ).UniqueResult<Int32>();  
+            }
+
             IEnumerable<T> IContentQuery<T>.Slice(int skip, int count) {
                 return _query.Slice(skip, count).AsPart<T>();
             }

src/Orchard/ContentManagement/IContentQuery.cs

@@ -16,6 +16,7 @@ namespace Orchard.ContentManagement {
 
         IEnumerable<TPart> List();
         IEnumerable<TPart> Slice(int skip, int count);
+        int Count();
 
         IContentQuery<TPart, TRecord> Join<TRecord>() where TRecord : ContentPartRecord;