Fix indexing into tree with trailing slash

LibGit2Sharp.Tests/TreeFixture.cs

@@ -241,6 +241,31 @@ public void CanRetrieveTreeEntryPath()
             }
         }
 
+        [Fact]
+        public void CanUseTrailingSlashToIndexIntoSubtree()
+        {
+            var path = SandboxBareTestRepo();
+            using (var repo = new Repository(path))
+            {
+                var tree = repo.Lookup<Tree>(sha);
+                Assert.False(tree.IsMissing);
+
+                var treeEntry1 = tree["1/"];
+                var treeEntry2 = tree["1"];
+
+                Assert.NotNull(treeEntry1);
+                Assert.NotNull(treeEntry1.Target);
+                Assert.NotNull(treeEntry2);
+                Assert.NotNull(treeEntry2.Target);
+
+                Assert.Equal(treeEntry1.Name, treeEntry2.Name);
+                Assert.Equal(treeEntry1.TargetType, treeEntry2.TargetType);
+                Assert.Equal(treeEntry1.Target.Sha, treeEntry2.Target.Sha);
+                Assert.Equal(treeEntry1.Mode, treeEntry2.Mode);
+                Assert.Equal(treeEntry1.Path, treeEntry2.Path);
+            }
+        }
+
         [Fact]
         public void CanParseSymlinkTreeEntries()
         {

LibGit2Sharp/Tree.cs

@@ -68,8 +68,9 @@ private unsafe TreeEntry RetrieveFromPath(string relativePath)
                     return null;
                 }
 
-                string filename = relativePath.Split('/').Last();
-                string parentPath = relativePath.Substring(0, relativePath.Length - filename.Length);
+                string trimmed = relativePath.TrimEnd('/');
+                string filename = trimmed.Split('/').Last();
+                string parentPath = trimmed.Substring(0, trimmed.Length - filename.Length);
                 return new TreeEntry(treeEntry, Id, repo, Tree.CombinePath(path, parentPath));
             }
         }