NCR_Tree: fix rbt removal, again.
NameCache: fix clean_by_threshold.
NCR_Tree: fix rbt removal.
NameCache::bucket_init: initialize bucket for tree.

* insert: add parameter to skip insert record to the list.
* insert_raw: add parameter to skip cleanup and inserting record to
  the list.
*
Rescached: load hosts file.
libvos: submodule update.