ln: Use basename when target directory is specfied

The following should work, but without this patch, it tries
to create the link as x/y and it fails with EEXIST.

$ mkdir -p x/y
$ ln -s -t . x/y

src/ln/ln.rs

@@ -189,7 +189,16 @@ fn link_files_in_dir(files: &[PathBuf], target_dir: &PathBuf, settings: &Setting
     let mut all_successful = true;
     for srcpath in files.iter() {
         let targetpath = match srcpath.as_os_str().to_str() {
-            Some(name) => target_dir.join(name),
+            Some(name) => {
+                match Path::new(name).file_name() {
+                    Some(basename) => target_dir.join(basename),
+                    // This can be None only for "." or "..". Trying
+                    // to create a link with such name will fail with
+                    // EEXIST, which agrees with the bahavior of GNU
+                    // coreutils.
+                    None => target_dir.join(name),
+                }
+            }
             None => {
                 show_error!("cannot stat '{}': No such file or directory",
                             srcpath.display());

tests/test_ln.rs

@@ -1,6 +1,5 @@
 use common::util::*;
 
-
 #[test]
 fn test_symlink_existing_file() {
     let (at, mut ucmd) = at_and_ucmd!();
@@ -248,6 +247,32 @@ fn test_symlink_target_dir() {
     assert_eq!(at.resolve_link(file_b_link), file_b);
 }
 
+#[test]
+fn test_symlink_target_dir_from_dir() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    let dir = "test_ln_target_dir_dir";
+    let from_dir = "test_ln_target_dir_from_dir";
+    let filename_a = "test_ln_target_dir_file_a";
+    let filename_b = "test_ln_target_dir_file_b";
+    let file_a = &format!("{}/{}", from_dir, filename_a);
+    let file_b = &format!("{}/{}", from_dir, filename_b);
+
+    at.mkdir(from_dir);
+    at.touch(file_a);
+    at.touch(file_b);
+    at.mkdir(dir);
+
+    ucmd.args(&["-s", "-t", dir, file_a, file_b]).succeeds().no_stderr();
+
+    let file_a_link = &format!("{}/{}", dir, filename_a);
+    assert!(at.is_symlink(file_a_link));
+    assert_eq!(&at.resolve_link(file_a_link), file_a);
+
+    let file_b_link = &format!("{}/{}", dir, filename_b);
+    assert!(at.is_symlink(file_b_link));
+    assert_eq!(&at.resolve_link(file_b_link), file_b);
+}
+
 #[test]
 fn test_symlink_overwrite_dir() {
     let (at, mut ucmd) = at_and_ucmd!();