Make dirname and basename ignore trailing separators and double slashes.

Separators are still preserved for other path methods.

Review URL: https://codereview.chromium.org//11638021

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/path@16397 260f80e4-7a28-3924-810f-c04153c831b5
3 files changed
tree: 6f5dd5169b0e8244e5c43b1f1497f0164c48b7a5
  1. lib/
  2. test/
  3. pubspec.yaml