Fixed: bug that getHttpResponseGET and getHttpResponsePOST do not handle http request
Change: verify using the same version of md5Sign function
Change: callback(false) directly  when verify failed
Change: merged TRADE_FINISHED and TRADE_SUCCESS event, only emit create_direct_pay_by_user_trade_success event [ref](http://club.alipay.com/read-htm-tid-9970794.html)
Change: increased version number