Logger must be in its own process

 File handles held by the parent are duplicated when a new process
 is created

 This means that both the main and all child processes get
 a copy of the log file's file handle, which causes file-lock
 problems when trying to rotate/move the log file.

 The solution is to create a child process which opens the file.
 This process never generates any child processes, so there is only
 one file handle for the log file.