Fix Directory, File and Link constructor text.

sdk/lib/io/link.dart

Index: sdk/lib/io/link.dart
diff --git a/sdk/lib/io/link.dart b/sdk/lib/io/link.dart
index 13c18693f53c39e9a7309526c0f6a3f073920c08..18e5dc01f64faa24cfdf694f88d871e92bb95c73 100644
--- a/sdk/lib/io/link.dart
+++ b/sdk/lib/io/link.dart
@@ -15,9 +15,11 @@ abstract class Link extends FileSystemEntity {
   factory Link(String path) => new _Link(path);
 
   /**
-   * Create a Lint object from a URI.
+   * Creates a [Link] object.
    *
-   * If [uri] cannot reference a link this throws [UnsupportedError].
+   * The path is either an absolute path,
+   * or it is a relative path which is interpreted relative to the current
+   * working directory (see [Directory.current]).
    */
   factory Link.fromUri(Uri uri) => new Link(uri.toFilePath());