missing support for logging

Binary package hint: python-daemon

The attached patch adds logging support: it is now possible to use logging.Logger instances alongside files in the options "files_preserve", "stdout", and "stderr". DaemonContext.open() then keeps the files used by the listed loggers open and also is able to redirect stdout and stderr to a logger instance in alternative of to a file. One important use case for this is to use logging.handlers.RotatingFileHandler to handle stdout/stderr. This avoids potential problems when the files get really big [1] and the daemon may have to be stopped to rotate the files manually.

[1] http://mail.python.org/pipermail/tutor/2005-July/040008.html