A handler for logging to a file, which watches the file
to see if it has changed while in use. This can happen because of
usage of programs such as newsyslog and logrotate which perform
log file rotation. This handler, intended for use under Unix,
watches the file to see if it has changed since the last emit.
(A file has changed if its device or inode have changed.)
If it has changed, the old file stream is closed, and the file
opened to get a new stream.
This handler is not appropriate for use under Windows, because
under Windows open files cannot be moved or renamed - logging
opens the files with exclusive locks - and so there is no need
for such a handler.
This handler is based on a suggestion and patch by Chad J.
Schroeder.