When a command has positional varargs, keep offering the configured
completion for each successive argument.
Right now this only influences `config-cycle`.
Previously, `config-cycle <option> ` would offer a value completion for
only the first argument after the option. Now it will keep offering
value completion for each successive argument.
This will be useful for passing multiple tags to the new bookmark
commands that will be added for #882.
f237a87ad0