Fix roundup-server logging for Python 3.

Using the roundup-server support for redirecting output to a log file
fails with Python 3:

    sys.stdout = sys.stderr = open(self["LOGFILE"], 'a', 0)
ValueError: can't have unbuffered text I/O

Thus, this patch switches that redirection to use line-buffered output
(1 as third argument to open), which works with both Python 2 and
Python 3.

Author: jsm28

roundup/scripts/roundup_server.py

@@ -674,8 +674,9 @@ def trackers(self):
 
     def set_logging(self):
         """Initialise logging to the configured file, if any."""
-        # appending, unbuffered
-        sys.stdout = sys.stderr = open(self["LOGFILE"], 'a', 0)
+        # appending, line-buffered (Python 3 does not allow unbuffered
+        # text files)
+        sys.stdout = sys.stderr = open(self["LOGFILE"], 'a', 1)
 
     def get_server(self):
         """Return HTTP server object to run"""