byterange: backport fix from upstream

mercurial/byterange.py

@@ -261,6 +261,8 b' class FTPRangeHandler(urllib2.FTPHandler'
         host, port = splitport(host)
         if port is None:
             port = ftplib.FTP_PORT
+        else:
+            port = int(port)
 
         # username/password handling
         user, host = splituser(host)