It won't block them, it just asks please don't visit these files/folders.
Google is usually friendly though, and usually obeys robots.txt.
To the OP: Keep in mind it may take a few days before you see the obedience.
It's just symantics , if you go to your Google Webmaster tools it doesn't say "Kindly asked not to look at these locations" it says "blocked by robots.txt".....i like blocked it sounds so much meaner