Revert "http: remove bodyHead from 'upgrade' events"

This reverts commit a40133d10cdb911b27fe8d46d67a835b0103bbf1.

Unfortunately, this breaks socket.io.  Even though it's not strictly an
API change, it is too subtle and in too brittle an area of node, to be
done in a stable branch.

Conflicts:
	doc/api/http.markdown