Fix generic, Debian, Ubuntu,  and FreeBSD installation instruction
    * Generic: align file layout with other installation instructions
    * Debian: ensure that debhelper, cdbs, autotools-dev is installed
    * Ubuntu, Debian: aptitude is not part of baseline installation. use
      apt-get instead
    * FreeBSD: fix typo, fix path for libpcap
Merge pull request #3 from alexander-zimmermann/master

Docs: fix generic, Debian, Ubuntu, and FreeBSD installation instruction