Log Message:
Update rake to 0.7.3.

Changes since 0.7.1:
* Error messages are now send to stderr rather than stdout (from
  Payton Quackenbush).
* Better error handling on invalid command line arguments (from Payton
  Quackenbush).
* Added rcov task and updated unit testing for better code coverage.
* Fixed some bugs where the application object was going to the global
  appliation instead of using its own data.
* Added square and curly bracket patterns to FileList#include (Tilman
  Sauerbeck).
* Added plain filename support to rule dependents (suggested by Nobu
  Nakada).
* Added pathmap support to rule dependents.
* Added a 'tasks' method to a namespace to get a list of tasks
  associated with the namespace.
* Fixed the method name leak from FileUtils (bug found by Glenn
  Vanderburg).
* Added rake_extension to handle detection of extension collisions.
* Added test for noop, bad_option and verbose flags to sh command.
* Removed dependency on internal fu_xxx functions from FileUtils.
* Added a 'shame' task to the Rakefile.
* Added tar_command and zip_command options to the Package task.
* Added a description to the gem task in GemPackageTask.
* Fixed a bug when rules have multiple prerequisites (patch by Joel
  VanderWerf)
* Added a protected 'require "rubygems"' to test/test_application to
  unbreak cruisecontrol.rb.
* Added the handful of RakeFileUtils to the private method as well.
* Added block based exclusion.
* The clean task will no longer delete 'core' if it is a directory.
* Removed rake_dup.  Now we just simply rescue a bad dup.
* Refactored the FileList reject logic to remove duplication.
* Removed if __FILE__ at the end of the rake.rb file.
* Added existing and existing! methods to FileList
* FileLists now claim to be Arrays (via is_a?) to get better support
  from the FileUtil module.
* Added init and top_level for custom rake applications.