Revert "Check for mocha gem without requiring the lib. [#403 state:resolved]"

This reverts commit 4d5ac3f3d2e1667971752c9a4e536de1a5bec364.

activesupport/lib/active_support/testing/setup_and_teardown.rb

@@ -18,9 +18,9 @@ def self.included(base)
             alias_method :run, :run_with_callbacks_and_miniunit
           else
             begin
-              gem 'mocha'
+              require 'mocha'
               alias_method :run, :run_with_callbacks_and_mocha
-            rescue Gem::LoadError
+            rescue LoadError
               alias_method :run, :run_with_callbacks_and_testunit
             end
           end