Try to include the autoload.php file from different locations

Check for the autoload file on multiple locations, so the vendor/bin script does not break when the symlink is followed into the vendors package dir.

When I run `vendor/bin/pdepend` now, I get:
```shell
Warning: require_once(/Users/jachim/project/vendor/pdepend/pdepend/src/bin/../../vendor/autoload.php): failed to open stream: No such file or directory in /Users/jachim/project/vendor/pdepend/pdepend/src/bin/pdepend on line 52
```