avoid circular reverse self-dependencies

Packdeps' reverse dependencies output currently lists self-dependencies.  Eg:

http://packdeps.haskellers.com/reverse/Agda
http://packdeps.haskellers.com/reverse/pandoc

This patch fixes the reverse output so that self-dependencies are no longer listed.  I tested it locally and it seems to fix the problem for me.
yesod 1.2
Manual ungzipping #17
Merge branch 'patch-1' of https://github.com/juhp/packdeps into web
Updated copy-to location