fails:Syslog.mask returns the log priority mask
fails:Syslog.mask defaults to 255
fails:Syslog.mask returns nil if the log is closed
fails:Syslog.mask persists if the log is reopened
fails:Syslog.mask= sets the log priority mask
fails:Syslog.mask= raises an error if the log is closed
fails:Syslog.mask= only accepts numbers
fails:Syslog.mask= persists if the log is reopened
