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

@@ -22,13 +22,19 @@ module Webrat #:nodoc:
 
     def post(url, data, headers_argument_not_used = nil)
       post_data = data.inject({}) do |memo, param|
-        case param.last
+        case param
         when Hash
-          param.last.each {|attribute, value| memo["#{param.first}[#{attribute}]"] = value }
-        else
-          memo[param.first] = param.last
+          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 }
+          else
+            memo[param.first] = param.last
+          end
+          memo
         end
-        memo
       end
       @response = mechanize.post(url, post_data)
     end