Added option to do data and attachment directory hashing, up to four levels. Will...

Added option to do data and attachment directory hashing, up to four levels. Will automatically search for missing file at other levels, move them to the right place, create hash directories, etc.

Should work for both data directory and attachment. Also modified Squirrelspell plugin to use this as well.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@1857 7612ce4b-ef26-0410-bec9-ea0150e637f0