Revert "Merge pull request #259 from sledgehammer999/revert_disk_cache"

This reverts commit a796df9019878320f11df72d08f2f31921c09217.
Allow control of cache expiry interval (libtorrent 0.16.10 allocator can now return cache to kernel)
Merge pull request #653 from Gelmir/evict_cache

Allow controling cache expiry timer