PHPUnit autoload file for PhpStorm

PHPUnit autoload file for PhpStorm

`autoload.ide.php` is PhpUnit entry point for PhpStorm IDE
and other JetBrains IDEs.
This file should be set in `Languages and frameworks > PHP > PhpUnit`
select `Use Composer autoloader` and set `Path to script` to `tests/phpunit/autoload.ide.php`

After that, tests can be run in PhpStorm using Right-click > Run
or `Ctrl + Shift + F10`. Also, tests can be run with debugger.

`autoload.ide.php` basically  does almost the same thing
as `tests/phpunit/phpunit.php`,
except that all code is executed inside some function, so some hacks
needed to make old code to be executed as if it was executed on top
of the execution stack.

PS: Mostly it is copy-paste from `phpunit.php` and `doMaintenance.php`.

Change-Id: Idcee38d149542f747ed52c8c9491c6651a0581d9