- Fix caching of descriptor lists in Storage Plugin. Address
associated things like replacement policy, etc.

- Additional tests
   - Delayed writing to better test swarming in SET
   - symlinks;  verify file permissions, etc. with gcp

- Metadata passing

   * get_init (noop storage plugin for get_*)
   * ggcmd
   * pass (ggcmd result) to get_chunk RPC
   
   * postfix / external interface work

- Add version information to the OID


