v0.91
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* The 'category' field for objects has been removed.  This was originally added
  to track PG stat summations over different categories of objects for use by
  radosgw.  It is no longer has any known users and is prone to abuse because it
  can lead to a pg_stat_t structure that is unbounded.  The librados API calls
  that accept this field now ignore it, and the OSD no longers tracks the
  per-category summations.

* The output for 'rados df' has changed.  The 'category' level has been
  eliminated, so there is now a single stat object per pool.  The structure of
  the JSON output is different, and the plaintext output has one less column.

* The 'rados create <objectname> [category]' optional category argument is no
  longer supported or recognized.

* rados.py's Rados class no longer has a __del__ method; it was causing
  problems on interpreter shutdown and use of threads.  If your code has
  Rados objects with limited lifetimes and you're concerned about locked
  resources, call Rados.shutdown() explicitly.

* There is a new version of the librados watch/notify API with vastly
  improved semantics.  Any applications using this interface are
  encouraged to migrate to the new API.  The old API calls are marked
  as deprecated and will eventually be removed.

* The librados rados_unwatch() call used to be safe to call on an
  invalid handle.  The new version has undefined behavior when passed
  a bogus value (for example, when rados_watch() returns an error and
  handle is not defined).

v0.92
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