fix against corrupted output in parallel logging

fix against corrupted output in parallel logging

In 825607672215b7a12ea6e201a89cd5209f6d657f it was attempted to fix
a bug previously introduced by logging related changes.  The problem
is that a va_list can be corrupted after it has been used once, so
we need to va_copy before each successive use.

And if we copy it, we also need to use the copy, and not the original ;)