Enable stdio inheritance.

Enable inheritance for stdio file descriptors in daemon mode. It allows
you in daemon mode to redirect the output to a file if needed.

By default in daemon mode gunicorn will close all file handle except if
you pass the "-R" options. In this cases STDIO will be preserved.

fix #309
only close 0-2 fds when -R isn't specified

Following some discussion on IRC with @GrahamDumpleton this patch only
close stdios if -R isn't specified. It also let others fds open and
don't try to close them.

This should fix logging around and behave like other daemons. It should
also close #309.
Ensure that detaching from controlling terminals, but allow for redirection to files.
document the use of PYTHONUNBUFFERED in config