[FreeBSD] replace pkg_version with pkg_info, for checking a package installed.

It would be better to use __pkg_info__ for checking whether a package is installed.

There is a reason why, 

 * Both pkg_version and pkg_info are part of the base OS.
 * pkg_info is faster than pkg_version, listing up installed packages.

```
$ time pkg_version -Xs zsh
zsh                                 =
pkg_version -Xs zsh  0.20s user 0.18s system 104% cpu 0.357 total

$ time pkg_info -Ix zsh
zsh-5.0.2_1         The Z shell
pkg_info -Ix zsh  0.01s user 0.01s system 94% cpu 0.017 total
```