animation module fails with KeyError: 'twh-delay'

[mbaldessari]

./captcp.py animation test.pcap -f 13.1 --output-dir foo
# captcp 2010-2013 Hagen Paul Pfeifer (c)             
# http://research.protocollabs.com/captcp/            
# connection: 13 (local flow: 1, remote flow: 2)      
Traceback (most recent call last):                    
  File "./captcp.py", line 5210, in <module>          
    sys.exit(captcp.run())                            
  File "./captcp.py", line 5191, in run               
    pcap_parser.run()                                 
  File "./captcp.py", line 562, in run                
    self.callback(dt, packet.data)                    
  File "./captcp.py", line 4360, in process_packet    
    self.process_local_side(ts, packet, tpi)          
  File "./captcp.py", line 4302, in process_local_side                   
    (td, len(packet) / 2, self.rtt_data["twh-delay"] / self.acceleration))
KeyError: 'twh-delay'