FreeBSD support

This is an attempt at adding FreeBSD support to the build system.  I'm sure we've made a few mistakes, and there's a few issues left to resolve:

From Pawel Tomulik who helped me push this over the finish line to a working package:

    things to consider:

      - I don't know what I'm doing :) , but:
      - it seems that vagrant-installers is self contained and needs no
        dependencies, if hower it do need some external packages, these
        should be listed under `deps:` in +MANIFEST,
      - currently vagrant installs into `/opt` which is bad choice for
        FreeBSD IMHO, should land somewhere within `/usr/local`,
      - don't know why, but it also builds a `*.zip` file in the dist
        directory,

    How to proceed:

         ./run 1.4.2 1.4.2 /tmp/test
         pkg add /tmp/test/vagrant-1.4.2.txz
         LD_LIBRARY_PATH=/opt/vagrant/embedded/lib vagrant

    Of course, the LD_LIBRARY_PATH=.. is a workaround. It should be fixed
    somehow.

I wanted to get this in for an early review/help from people that know what they are doing.