Add the find expressions for pruning the 'but-not' path to $@, to ensure
that each is seen as a separate argument. One one machine I had trouble
where the entire $prune variable was seen as a single expression i.e.

find: unknown predicate `-path /home/git/.gitolite/logs -prune -o'

In retrospect that seems obvious: what's less obvious is why it appeared
to work on my dev machine.