Description:
------------
`__DIR__`, `__FILE__` and `realpath()` now reveal physical path for virtual drives created with `subst` under Windows. This is a breaking backward-incompatible change.

The Windows’ built-in `subst` application maps a physical directory to a virtual drive and is used by Denwer for creating a virtual drive that web servers are virtually located on. Denwer is a WAMP kit popular in Russia.

Documentation pages for `__DIR__`, `__FILE__` and `realpath()` have no information about this change.

PHP 7.2.12 works as expected: virtual-drive path is returned, physical path is not revealed.

So either the behavior in PHP 7.3.x should be the same as in PHP 7.2.x (virtual-drive path returned, physical-drive path not revealed), or this breaking change should be documented.

For example, in PHP 7.3.0 (with the latest Apache 2.4.37 [2018-11-21] from Apache Lounge):

	__DIR__:
		D:\_webservers\home\test-host

	__FILE__:
		D:\_webservers\home\test-host\test.php

	$_SERVER['DOCUMENT_ROOT']:
		Z:/home/test-host/www

	realpath($_SERVER['DOCUMENT_ROOT']):
		D:\_webservers\home\test-host\www

While in PHP 7.2.12:

	__DIR__:
		Z:\home\test-host

	__FILE__:
		Z:\home\test-host\test.php

	$_SERVER['DOCUMENT_ROOT']:
		Z:/home/test-host/www

	realpath($_SERVER['DOCUMENT_ROOT']):
		Z:\home\test-host\www


Test script:
---------------
<?php

echo __DIR__ . '<br>'
   . __FILE__ . '<br>'
   . $_SERVER['DOCUMENT_ROOT'] . '<br>'
   . realpath($_SERVER['DOCUMENT_ROOT']);