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.
stats: atomically set sort_status
stats: it's fine to use asserts in internal functions
misc: fixed mistype: Sainity -> Sanity
blob: do not depend on dirname implementation

Also use snprintf() so we always get NULL-terminated string.
blob: do not place ctl->thread_num in register
blob: loff_t is used only in __linux__ code
blob: do not place want_defrag in register
mobjects: protect against malloc size overflow
blob: added periodic comments
data-sort: added leak note