X86 64

Hi Fred,

Compiling on Ubuntu 12.04 on a 64-bit machine I ran into this error from configure:
    checking for libpcap... configure: error: Unable to find matching library for header file in /usr

This should fix the problem. I wasn't sure if you wanted the configure changes in the same patch as the configure.ac patch. I've done them separately as I seem to have different versions of autoconf/automake to you. Feel free to replace that patch with whatever you feel is appropriate.