Reposition log file pointer assignment to avoid race condition.

Currently this is not a problem as the client is single threaded
and the server hasn't spawned any threads at the time it calls
log_init_stream(), but in the future... .

git-svn-id: svn://daper.net/moc/trunk@2597 910807d9-36e0-0310-a014-e9ea483e2ba4
Warn that using digits as keys may be disallowed in the future.

git-svn-id: svn://daper.net/moc/trunk@2598 910807d9-36e0-0310-a014-e9ea483e2ba4