Make memoization of the svn:mergeinfo processing functions persistent with
Memoize::Storable so that the memoization tables don't need to be regenerated
every time the user runs git-svn fetch.
The Memoize::Storable hashes are stored in ENV{GIT_DIR}/svn/.caches.
[ew: changed caches path to avoid conflicts with old repos]
[ew: File::Path::{make_path => mkpath} for compatibility]
[ew: line-wrapped at 80 chars]
Acked-by: Eric Wong <normalperson@yhbt.net> Signed-off-by: Andrew Myrick <amyrick@apple.com>