Implement variables order

This also makes cli mode consist with PHP if S&E is not
in variables_order $_SERVER/$_ENV will not available in cli.

before the diff HHVM's variables_order=SEGPC and request_order=GPC
after the diff thoes directive are default one:

 - variables_order=EGPCS
 - request_order=  and it will be the same as variables_order

@see <http://php.net/manual/en/ini.core.php#ini.variables-order>

PHP distributed with dev and prod config, so after the diff we may
need to explictly set those directive to avoid useless computation.
(if we use the php.ini shiped with PHP then they will the same)

> The test cases didn't test `$_REQUEST` variable, I didn't find a proper way to do that.