Bug 5036: capital 'L's in logs when daemon queue overflows (#576)

Bug 5036: capital 'L's in logs when daemon queue overflows (#576)

Varying number of capital 'L's have been observed in access logs
written by the daemon module.  The 'L's corresponded with the
cache log message:

  "queue is too large; some log messages have been lost."

This was caused by the fact that the 'L' command byte was
buffered even when the queue was too large to accept messages.

Deferring buffering the command byte until just before the
message itself is buffered.