Fix Directory, File and Link constructor text.

sdk/lib/io/directory.dart

Index: sdk/lib/io/directory.dart
diff --git a/sdk/lib/io/directory.dart b/sdk/lib/io/directory.dart
index e977d2fe86b0cf2966c6f498b179f77e69ab72ba..eecaa685996621db16f8a1b3b1306f95bd4c2de0 100644
--- a/sdk/lib/io/directory.dart
+++ b/sdk/lib/io/directory.dart
@@ -118,9 +118,13 @@ abstract class Directory extends FileSystemEntity {
   final String path;
 
   /**
-   * Creates a directory object. The path is either an absolute path,
-   * or it is a relative path which is interpreted relative to the directory
-   * in which the Dart VM was started.
+   * Creates a [Directory] object.
+   *
+   * If [path] is a relative path, it will be interpreted relative to the
+   * current working directory (see [Directory.current]), when used.
+   *
+   * If [path] is an absolute path, it will be immune to changes to the
+   * current working directory.
    */
   factory Directory(String path) => new _Directory(path);