FreeBSD: pkgng

This two patches adding support for the current package system of FreeBSD 10 and above. The first patch adds support for resolving dependencies with packages and the second patch adds the client tool. The package verification on the client is a bit slow, because it is calling "pkg search" for each package to get the candidate version, but it is working correctly.

This implementation requires the client to be in the x86:64 or x86:32 group, because that's the arch component in the URL for the pkg repo. The default freebsd 10 pkg repo could be added with this source entry:

    <Source type='pkgng'
            url='http://pkg.freebsd.org/'
            version='10'>
      <Component>latest</Component>
      <Arch>x86:64</Arch>
      <Arch>x86:32</Arch>
    </Source>