Ignore ErrClosedPipe for stdin in Container.Attach.

But pass `err` in the error channel anyway; don't ignore it anymore.
Closes #2328 - allow the user to specify a string timestamp (not just a unix epoch) in the string format that the docker cli shows to the user
Merge branch '2328-docker-events-since-date-string' of github.com:SvenDowideit/docker into 2328-docker-events-since-date-string