Fixed BUILD_TARGET verification in package.sh.
package.sh: Updated build for FreeBSD.

Introducing freebsd-port and freebsd-standalone parameter.
In FreeBSD, port can only access internets on fetch stage.
Automated dependency fetch is impossible during port build.
Therefore Power and CuraEngine becomes separate packages and they
are not fetched/build when freebsd-port parameter is given.
Use freebsd-standalone if you want to build your own local bundle.