* pkg/log: fix data race on d

Wrap d in a mutex to prevent data race. This makes is slower, but this
is a debugging aid anyway. It's not used normally.
Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix tests compilation
Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix test compile
Signed-off-by: Miek Gieben <miek@miek.nl>