Util: Change debug method to avoid using buildin session method
Util: Make dummy header() to avoid calling building method

If some method which will change output header is called, PHPUnit will report
error like:

    Cannot modify header information - headers already sent by (output started
    at phar:///usr/local/bin/phpunit/phpunit/Util/Printer.php:172)

So we can only overwrite these system buildin functions.
Util: Add getter method of session id
Util: Add cookie relate methods