The spec says:
> The client name, clientname, MUST be a non-empty string of ASCII digits,
> letters, dots and/or underscores, starting with a letter, and without sets
> of two consecutive dots or a dot followed by a digit.
Sjoerd points out that this is too restrictive - every context in which we mention client names is allowed to start with "_" - so when we're breaking D-Bus API anyway, we should apply s/starting with a letter/& or an underscore/ here.
This is such a small change that we should just do it as part of Bug #23148, I think.
*** This bug has been marked as a duplicate of bug 23148 ***