Perf Improvement: don't digest after the $timeout.

As far as I can tell, the `$timeout` in the directive does not actually modify any code that would require a `$digest`, although `$timeout` automatically calls digest at the end of the function.

This causes unnecessary digests to happen too frequently on startup (when I have several `ui-sortable` directives), affecting my startup performance.

It seems to work to call `$timeout(callbac, 0, false)` which forgoes the `$digest` but everything still works.

I there any reason that this won't work in your `link` function?