commands: move checkformat to bookmarks module commands.bookmark has grown quite large with two closures already. Let's split this up (and in the process allow extensions to override the default behavior).

tests: tell pip not to check for a newer version pip will check to see if it's the latest version, and complain if it isn't. The --no-index flag implies the --disable-pip-version-check flag, and makes the warning (and any associated network activity) go away.