fetch: allow -r for remote repos

filelog encoding: move the encoding/decoding into store the escaping of directories ending with .i or .d doesn't really belong to filelog. we put the encoding/decoding in store instead, for backwards compat, streamclone and the fncache file format still uses the partially encoded filenames.

store: refactor the fncache handling put all the fncache file writing and reading in the same place.