Set hash value instead of merge a single key, and use flatten! if possible

There's no need to create two extra hashes with options.merge(another_hash),
with the goal of setting only one value, so lets just set it.

Also refactor validates_each to use _merge_attributes, like other
validates_* helpers do.

activemodel/lib/active_model/validations.rb

@@ -82,8 +82,7 @@ module ClassMethods
       #   <tt>:unless => Proc.new { |user| user.signup_step <= 2 }</tt>). The
       #   method, proc or string should return or evaluate to a true or false value.
       def validates_each(*attr_names, &block)
-        options = attr_names.extract_options!.symbolize_keys
-        validates_with BlockValidator, options.merge(:attributes => attr_names.flatten), &block
+        validates_with BlockValidator, _merge_attributes(attr_names), &block
       end
 
       # Adds a validation method or block to the class. This is useful when

activemodel/lib/active_model/validations/with.rb

@@ -3,8 +3,10 @@ module Validations
     module HelperMethods
       private
         def _merge_attributes(attr_names)
-          options = attr_names.extract_options!
-          options.merge(:attributes => attr_names.flatten)
+          options = attr_names.extract_options!.symbolize_keys
+          attr_names.flatten!
+          options[:attributes] = attr_names
+          options
         end
     end