Ruby mogilefs-client 3.1.0

* improved API support for uploading large files
  While we've always supported uploading large files, the
  (still-supported) existing APIs were somewhat awkward or
  required the file to exist on the file system.  See
  MogileFS::NewFile for details and examples.

* more informative exception messages for timed-out requests

* :fail_timeout parameter, the timeout for retrying a failed
  tracker connection.  This defaults to 5 seconds (same as
  previous versions where this was hard-coded.

* :new_file_max_time parameter
  Controls the maximum of time spent creating and uploading
  a new file in MogileFS.   This defaults to 1 hour (which
  matching the expiry time of a row in the MogileFS internal
  tempfile table).

* store_file works on unlinked File/Tempfile objects

* each_fid method in MogileFS::Admin fixed

* stale_fid_checker example script added

* mogstored_rack example split into a standalone RubyGem:
  http://bogomips.org/mogstored_rack/

* backend error constants are generated on const_missing,
  instead of when raised, making it easier to rescue exceptions
  we didn't explicitly enable

* some internal cleanups and documentation improvements