Make code statistics rake task handle new test locations properly

As of 2a68f68:

- Unit tests are now in test/models, instead of test/units
- Functional tests are now in test/controllers, instead of
  test/functional
- Helper tests are now in test/helpers, instead of test/units/helpers
- Mailer tests are now in test/mailers, instead of test/functional

Update the rake task for code statistics (`rake stats`) so that it
recognizes files in the above locations as tests, and accurately
calculates statistics such as "Test LOC" and "Code to Test Ratio."
Safely handle Rails apps that still have tests in the old locations.

Author: georgeclaghorn

railties/lib/rails/code_statistics.rb

@@ -1,6 +1,12 @@
 class CodeStatistics #:nodoc:
 
-  TEST_TYPES = %w(Units Functionals Unit\ tests Functional\ tests Integration\ tests)
+  TEST_TYPES = ['Controller tests',
+                'Helper tests',
+                'Model tests',
+                'Mailer tests',
+                'Integration tests',
+                'Functional tests (old)',
+                'Unit tests (old)']
 
   def initialize(*pairs)
     @pairs      = pairs