1. add a feature that tcpcopy can replay process more than one pcap-file. the files should be created by tcpdump using -W -C option.
2. add a feature that tcpcopy can find a string in a packet, and then replace it with another string.
notice: file names should has the same length. such as cap00/cap01/.../cap09/cap10 is ok, but cap0/cap1/.../cap9/cap10/cap11 will stop at file "cap10".