url: clean up use of two-argument raise

This makes any attempt to port to Python 3 harder, and the new syntax
is supported in 2.4 already.

mercurial/url.py

@@ -164,7 +164,7 b' if has_https:'
                     if sock is not None:
                         sock.close()
 
-            raise socket.error, msg
+            raise socket.error(msg)
 
 class httpconnection(keepalive.HTTPConnection):
     # must be able to send big bundle as stream.