Avoid error message if --version flag is used.

samsara 戝 /tmp/Bitmask-linux64-0.3.3 
11726 ◯ : ./bitmask --version                                                                                                                                      
No updates found
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 42169)
Traceback (most recent call last):
  File "/tmp/Bitmask-linux64-0.3.3/lib/SocketServer.py", line 593, in process_request_thread
    self.finish_request(request, client_address)
  File "/tmp/Bitmask-linux64-0.3.3/lib/protobuf/socketrpc/server.py", line 243, in finish_request
    request, client_address, self, self.socket_rpc_server)
  File "/tmp/Bitmask-linux64-0.3.3/lib/protobuf/socketrpc/server.py", line 83, in __init__
    self, request, client_address, server)
  File "/tmp/Bitmask-linux64-0.3.3/lib/SocketServer.py", line 649, in __init__
    self.handle()
  File "/tmp/Bitmask-linux64-0.3.3/lib/protobuf/socketrpc/server.py", line 98, in handle
    self.request.shutdown(socket.SHUT_RDWR)
  File "/tmp/Bitmask-linux64-0.3.3/lib/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
error: [Errno 107] Transport endpoint is not connected
----------------------------------------
Bitmask version: 0.3.3

(from redmine: created on 2013-09-23, closed on 2013-09-24)