K/V fixes after stress-test :-)

- track block versions correctly - per inode block (128kb) instead of tree block (4kb)
- prevent multiple parallel CAS writes of the same inode block
- add logging for EILSEQ which means invalid data in the tree
- fix get_block updated flag which was true for blocks already in cache and was leading to infinite loops on "unrelated block" errors
- apply changes to blocks in cache only after successful writes (using "virtual changes")
- do not replace cached block with an older version from disk
- recheck "unrelated blocks" (read/update collisions) until data stops changing
- track tree path correctly - do not treat split block as parent of its right half
- correctly move blocks when finding new empty place on disk
- restart updates from the beginning when one of blocks is changed by a parallel update
- fix delete using SET opcode and setting key to the empty value instead
- prevent changing the same key more than 1 time in parallel
- fix listing verification
- resume continue_updates in update_find (required because it uses continue_update itself)
- add allow_old_cached parameter to get()

src/kv_db.h

@@ -21,7 +21,8 @@ struct kv_dbw_t
 
     uint64_t get_size();
 
-    void get(const std::string & key, std::function<void(int res, const std::string & value)> cb);
+    void get(const std::string & key, std::function<void(int res, const std::string & value)> cb,
+        bool allow_old_cached = false);
     void set(const std::string & key, const std::string & value, std::function<void(int res)> cb,
         std::function<bool(int res, const std::string & value)> cas_compare = NULL);
     void del(const std::string & key, std::function<void(int res)> cb,