Log Message:
Update ruby-i18n to 0.6.4.

* Include the key in "missing interpolation argument" errors.
* Update documentation for the `pluralize` method.  Hopefully made it
  clearer what is actually going on and why.
* Add parens to fix parse error in lib/i18n.rb in MagLev.
* Never modify the given options hash.
* Fix I18n.transliterate for non utf-8 keys (occurs e.g. in jruby
  1.7.0 which have US-ASCII encoded symbols).
* Do not overwrite response of first backend with later backends when
  looking up namespaces.
* Make exception message more helpful on YAML syntax error.
* Remove throwing `warning: invalid start is ignored`
  The last argument should be a Julian day number which denotes the
  day of calendar reform. Date::ITALY (2299161=1582-10-15),
  Date::ENGLAND (2361222=1752-09-14), Date::GREGORIAN (the proleptic
  Gregorian calendar) and Date::JULIAN (the proleptic Julian calendar)
  can be specified as a day of calendar reform
* Preventing transliterator constant from being modified for
  concurrency concerns.
* Revert "Fix i18n/backend/key_value to add data in a array" causing
  various issues.
* Add license information to gemspec.  This way you can get it when
  using rubygems.org API.
* Support Rails 4.
* Fixed Ruby 1.8 support due to missing `String#force_encoding`.
* Resolve problems with encoding and transliterator between various
  ruby versions.
* Do not do any utf8 conversion, assume valid data is received.