Normalize packages' library names.

This makes the library names play nicer with dartdoc.

Review URL: https://codereview.chromium.org//13674024

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/stack_trace@21106 260f80e4-7a28-3924-810f-c04153c831b5