Intern method with return a failed answer with given code and message

Property definitions

curl $ CurlRequest :: answer_failure
	# Intern method with return a failed answer with given code and message
	private fun answer_failure(error_code: Int, error_msg: String): CurlResponseFailed
	do
		return new CurlResponseFailed(error_code, error_msg)
	end
lib/curl/curl.nit:62,2--66,4