Clean up after r39484 and r39486.
Clean up after r39484 and r39486.

In particular, this adds CHANGELOG entries for packages that have been
modified and fixes pub's barback dependency so it doesn't declare
compatibility on an uncut release.

This releases args, barback, http_parser, and shelf.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//506973003

git-svn-id: 1179e775d7a957fb920f091aaff41c1e6b317097@39563 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/shelf,Joannis/shelf,dart-lang/shelf,Joannis/shelf,dart-lang/shelf