It was already unsigned in sudoers but not in the front-end or the
python plugin. Making this consistent resolves a lot of -Wconversion
warnings. Also clean up some other -Wconversion warnings in sudo_debug.c.
so python log system can be used with sudo logsystem.
Loggers use it by default (the handler is set on the root logger).
If that is not the intent, it can be overridden explicitly.
