Soft fail if reckon isn't configured by the time version.toString() is called

[ajoberstar]

As noted in #147, reckon sometimes isn't fully configured in time for other plugins that want to use the version.

One way to resolve this situation is to change the hard fail when reckon isn't fully configured to a soft fail. Return unspecified as the version value, but allow later attempts to use a reckoned version, presuming it is configured. Log a warning indicating reckon was evaluated too early (but only one of them) and log info level stacktraces each time it happens.