unable to tab complete machine names in subdirectories

This is totally my fault; I should have double checked this before issuing the pull request for #8. I'm unable to tab complete for matching machine names in subdirectories. I can probably fix this myself, but I don't know what `pwdmod2="${pwdmod2%/*}" ` is doing. 

This functionality apparently doesn't work in OS X. I added a [debugging branch](https://github.com/deanmalmgren/vagrant-bash-completion/tree/investigate-__vagrantinvestigate) with some [debugging statements in the __vagrantinvestigate function](https://github.com/deanmalmgren/vagrant-bash-completion/blob/3f74283fce3ad37fae93fb3cb1aa50d5307ab8fe/vagrant). This is what the output is in OS X:

```bash
[hal-9000 subdir/of/vagrant/box]$ __vagrantinvestigate 
recursion depth: 5
who are you pwdmod2? ''
who are you pwdmod2? ''
who are you pwdmod2? ''
who are you pwdmod2? ''
```