hash: fix eblob_hash_exit()

Properly free all data in hash.
Also renamed eblob_hash_exit() to eblob_hash_destroy() for consistency.
l2hash: do not depend on rb_node being first structure member

This adds more code, but it way more sane.
blob: fix possible segfault on OOB b->cfg.file access

Also add check for non-NULL b->cfg.file.
stats: atomically set sort_status
stats: it's fine to use asserts in internal functions
misc: fixed mistype: Sainity -> Sanity