Log Message:
Update ruby-pathname2 to 1.7.3.

== 1.7.3 - 24-Apr-2014
* The basename and dirname methods now return Pathname objects.

== 1.7.2 - 23-Apr-2014
* The join and expand_path methods now return Pathname objects.

== 1.7.1 - 28-Mar-2014
* Updated gemspec for Windows vs Unix.
* Updated README and MANIFEST.

== 1.7.0 - 28-Mar-2014
* Windows now uses FFI internally instead of win32-api.
* Added a custom pretty_print method for the pp library.
* Reorganized the test suite for Windows, and added many
  more test tasks to the Rakefile.