Support latest T4MVC 2.13.0

Latest T4MVC template uses ProjectItem.Collection which returns the ProjectItems that
contain the ProjectItem.

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/ProjectItem.cs

@@ -158,10 +158,15 @@ namespace ICSharpCode.PackageManagement.EnvDTE
 		
 		internal string GetIncludePath(string fileName)
 		{
-			string relativeDirectory = containingProject.GetRelativePath(projectItem.FileName);
+			string relativeDirectory = GetProjectItemRelativePathToProject();
 			return Path.Combine(relativeDirectory, fileName);
 		}
 		
+		string GetProjectItemRelativePathToProject()
+		{
+			return containingProject.GetRelativePath(projectItem.FileName);
+		}
+		
 		internal string GetIncludePath()
 		{
 			return projectItem.Include;
@@ -208,5 +213,21 @@ namespace ICSharpCode.PackageManagement.EnvDTE
 		public virtual short FileCount {
 			get { return 1; }
 		}
+		
+		public global::EnvDTE.ProjectItems Collection {
+			get {
+				string relativePath = GetProjectItemRelativeDirectoryToProject();
+				if (String.IsNullOrEmpty(relativePath)) {
+					return containingProject.ProjectItems;
+				}
+				var directoryProjectItem = new DirectoryProjectItem(containingProject, relativePath);
+				return directoryProjectItem.ProjectItems;
+			}
+		}
+		
+		string GetProjectItemRelativeDirectoryToProject()
+		{
+			return Path.GetDirectoryName(GetProjectItemRelativePathToProject());
+		}
 	}
 }

src/AddIns/Misc/PackageManagement/SharpDevelop.EnvDTE/Src/ProjectItem.vb

@@ -13,6 +13,7 @@ Namespace EnvDTE
 		ReadOnly Property Document() As Document
 		ReadOnly Property FileNames(index As Short) As String
 		ReadOnly Property FileCount() As Short
+		ReadOnly Property Collection As ProjectItems
 		
 		Sub Delete()
 		Sub Remove()

src/AddIns/Misc/PackageManagement/Test/Src/EnvDTE/ProjectItemTests.cs

@@ -372,5 +372,33 @@ namespace PackageManagement.Tests.EnvDTE
 			
 			Assert.AreEqual(1, count);
 		}
+		
+		[Test]
+		public void Collection_ProjectItemIsFileInProjectRootFolder_ReturnsProjectItemsCollectionForProject()
+		{
+			CreateProjectItems();
+			msbuildProject.FileName = @"d:\projects\MyProject\MyProject.csproj";
+			msbuildProject.AddFile(@"program.cs");
+			global::EnvDTE.ProjectItem projectItem = projectItems.Item("program.cs");
+			
+			global::EnvDTE.ProjectItems collection = projectItem.Collection;
+			
+			Assert.AreEqual(project.ProjectItems, collection);
+		}
+		
+		[Test]
+		public void Collection_ProjectItemIsFileInSubFolderOfProject_ReturnsProjectItemsCollectionForSubFolder()
+		{
+			CreateProjectItems();
+			msbuildProject.FileName = @"d:\projects\MyProject\MyProject.csproj";
+			msbuildProject.AddFile(@"src\program.cs");
+			global::EnvDTE.ProjectItem srcDirectoryItem = project.ProjectItems.Item("src");
+			global::EnvDTE.ProjectItem fileProjectItem = srcDirectoryItem.ProjectItems.Item("program.cs");
+			
+			global::EnvDTE.ProjectItems collection = fileProjectItem.Collection;
+			
+			global::EnvDTE.ProjectItem item = collection.Item("program.cs");
+			Assert.AreEqual("program.cs", item.Name);
+		}
 	}
 }