Simplify and speedup Hash#stringify_keys! References #10717 [Cheah Chu Yeow]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8576 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/lib/active_support/core_ext/hash/keys.rb

@@ -13,10 +13,7 @@ def stringify_keys
         # Destructively convert all keys to strings.
         def stringify_keys!
           keys.each do |key|
-            unless key.class.to_s == "String" # weird hack to make the tests run when string_ext_test.rb is also running
-              self[key.to_s] = self[key]
-              delete(key)
-            end
+            self[key.to_s] = delete(key)
           end
           self
         end