implemented a different approach to IO scheduling, so object->storage is no longer used, instead there is a queue and hash table of IO tasks to process, and it is always possible to know what are the scheduled and acrtive IO operations against every single key.

fixed a few bugs in DS store, now it's somewhat about able to reply to 'GET foo' with a bogus value.

cron part of disk store object cache implemented. Objects are pushed as IO jobs if needed, so that the IO thread will process them.

touched key for WATCH refactored into a more general thing that can be used also for the cache system. Some more changes towards diskstore working.