Don't clear all caches

After updating the node_access table by calling node_access_acquire_grants, this module also calls cache_clear_all();. On large sites, this causes an enormous performance hit. In my opinion, the cache should not be cleared.

I understand that some users expect to have caching, and yet see their changes immediately. Maybe this should be made optional?

If a cache clear must still happen, a more elegant approach might be to clear only the page cache, or target the cache_page table to remove only those URIs that refer to the updated nodes. But I don't think Flexi Access should concern itself with caching. That's better handled with other modules.