simplify file store path calculations

0.0x percent of paths are > 200 chars,
and 0.0x percent of users may want to look through their raw cache files
...
so nobody needs this, right ?

@apanzerj @rafaelfranca
Here's the best link I could find: http://unix.stackexchange.com/a/32834. Empirically 140 works for me too. It's definitely not ideal having to come up with a hard-coded lowest common denominator value for this :( I don't think there's a way to determine it at runtime either.