Fixes #92: symlinked items don't preserve file permissions

Let me know what you think. I'm looking to learn, so feel free to give me any suggestions you may have.

So you know, I couldn't chmod a symbolic link so I had to use umask to create the link with the correct permissions. Maybe I should add a comment to the code. I'm not sure if that is general knowledge.

I added a line to source the fs.sh file in the bats helper. I did so in order to gain access to the `octal_access` function in my tests. Let me know if there is a better way to do that.

Something else to note, I didn't handle the scenario where a file's access changes in git and the file is already linked. Should I add that to this PR or open a new issue?