Ruby mogilefs-client 3.2.0

Changes since 3.2.0-rc1 (MogileFS::Admin-only):

* admin supports "create_device" and "change_device_weight" commands

* admin casts "reject_bad_md5" field in "get_device" return
  value to boolean (true/false).

* minor code simplifications to admin

Changes since 3.1.1

* "list_keys" and "exist?" client commands raise errors properly
  on failure.

* backend connections no longer terminate on ERR responses, only
  on socket/connection errors.

* support the "updateclass" client command.  This is for updating
  the class of a given key and not to be confused with the
  "update_class" admin command.

* "new_file" checksum usage is now documented since MogileFS 2.60
  includes official support for checksums