Use `defadvice' rather than the new `nadvice` interface which is only
available in trunk. This fixes f71b5f7.

* projectile.el (projectile-compilation-find-file): Convert to `defavice'.
                (projectile-mode): Use ad-(de)activate.
Merge pull request #386 from daimrod/fix-compilation-find-file

Use `defadvice' rather than the new `nadvice` interface