Clean up dart:io exceptions.

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 dfe5637db0ac6247d1e57de90ff84e073c15812f..c8423b5032f35d60127d6f590bb9efef07c91dff 100644
--- a/sdk/lib/io/directory.dart
+++ b/sdk/lib/io/directory.dart
@@ -210,13 +210,13 @@ abstract class Directory implements FileSystemEntity {
 }
 
 
-class DirectoryIOException implements Exception {
-  const DirectoryIOException([String this.message = "",
+class DirectoryException implements IOException {
+  const DirectoryException([String this.message = "",
                               String this.path = "",
                               OSError this.osError = null]);
   String toString() {
     StringBuffer sb = new StringBuffer();
-    sb.write("DirectoryIOException");
+    sb.write("DirectoryException");
     if (!message.isEmpty) {
       sb.write(": $message");
       if (path != null) {