fix symlink creation for windows machines and problems with directory separator

Fix the symlink generation for Windows Machines.

Take care that Windows XP and older is not supported -> http://de2.php.net/manual/en/function.symlink.php

> Note: Windows users should note that this function will only work if the system you run PHP from is Windows Vista/Windows Server 2008 or newer. Windows versions prior to that does not support symbolic links.