Update ruby-pathname2 package to 1.6.4.

Update ruby-pathname2 package to 1.6.4.

== 1.6.4 - 20-Jan-2011
* Explicitly remove the Pathname const if it is already defined in order
  to avoid a superclass mismatch error. This library assumes that if you
  require pathname2, you want my version of the Pathname class.
* Updated URI handling for Ruby 1.9.x.
* Added the Pathname() method, a synonym for Pathname.new.
* Some Rakefile and gemspec tweaks.
* Some updates to the test suite, including some specifically for Windows 7.