fix post method in mechanize adapter to handle data as array or hash

it fixes spec/integration/mechanize/sample_app.rb:20

lib/webrat/adapters/mechanize.rb

@@ -22,6 +22,11 @@ module Webrat #:nodoc:
 
     def post(url, data, headers_argument_not_used = nil)
       post_data = data.inject({}) do |memo, param|
+        case param
+        when Hash
+          param.each {|attribute, value| memo[attribute] = value }
+          memo
+        when Array
           case param.last
           when Hash
             param.last.each {|attribute, value| memo["#{param.first}[#{attribute}]"] = value }
@@ -30,6 +35,7 @@ module Webrat #:nodoc:
           end
           memo
         end
+      end
       @response = mechanize.post(url, post_data)
     end