Adjust list_pkg_directories to always have / slashes so that we don't accidentally create escape characters on Windows.
Adjust list_pkg_directories to always have / slashes so that we don't accidentally create escape characters on Windows.

BUG=
R=rnystrom@google.com

Review URL: https://codereview.chromium.org//18238010

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@24827 260f80e4-7a28-3924-810f-c04153c831b5

dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk