Incorrect default autocomplete path

The use of base_path() and url() in the default value of apiAutoCompletePath causes the autocomplete to fail until a JSON file is generated. This problem isn't that serious as it only affects the availability of autocomplete before those JSON files are created (when api_shutdown is called and files need to be removed from the index).

I have tested the patch in both bare root (http://example.com/) and subdomain to make sure it works (http://example.com/api/). Autocomplete now works before those files are generated.