set FD_CLOEXEC on listening socket

Skype4Py uses os.execlp() to spawn skype if it is not yet started, this leaks
our listening FD to skype process and can't get it back even if we ourself exit
meanwhile.

and we can't startup again:
error: [Errno 98] Address already in use

Signed-off-by: Elan Ruusamäe <glen@delfi.ee>
Tested-by: Elan Ruusamäe <glen@delfi.ee>
--- bitlbee-3.0.5/protocols/skype/skyped.py~	2012-04-15 12:42:34.110550155 +0300
+++ bitlbee-3.0.5/protocols/skype/skyped.py	2012-04-15 13:50:51.089559368 +0300
@@ -31,6 +31,7 @@
 import hashlib
 from ConfigParser import ConfigParser, NoOptionError
 from traceback import print_exception
+from fcntl import fcntl, F_SETFD, FD_CLOEXEC
 import ssl
 
 __version__ = "0.1.1"
@@ -184,8 +185,10 @@
 	else:
 		sock = socket.socket()
 	sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+	fcntl(sock, F_SETFD, FD_CLOEXEC);
 	sock.bind((host, port))
 	sock.listen(1)
+
 	if hasgobject:
 		gobject.io_add_watch(sock, gobject.IO_IN, listener)
 	else: