FreeBSD 9.1 support + start daemons

The following commits add FreeBSD 9.1 support along side FreeBSD 9.0. They are both pretty much the same, all they do is provide the `_freebsd_90_` and `_freebsd_91_` methods which call a `_freebsd_9x_` function.

I've also added /etc/rc.conf enabling of the daemons as per the [FreeBSD Installation Instructions](http://docs.saltstack.org/en/latest/topics/installation/freebsd.html).

Another pass has been made on the DISTRO_NAME_L setting, FreeBSD doesn't seem to like the `sed -re 's/(\s)+/_/g'` method either though `sed -re 's/[[:space:]]+/_/g'` does seem to be working in both FreeBSD and Ubuntu for me.

I've changed the name of the "salt" FreeBSD package to "sysutils/py-salt" to reflect the new package name. You could also use "py27-salt" but the fully qualified port name has the advantage of supporting any future python version defaults used in the package repository.

As a potential fix for #20 I've added the ability for the pkgng PACKAGESITE variable to be set by the environment, I'm not too sure if the `VAR=${VAR:="default"}` syntax is plain POSIX or not though.

Apologies for this being a rather disjointed set of commits, if you'd like me to break them up a bit into more logical chunks I'll happily do so.