Using file operations on a symlink that points to a file outside the
directories being allowed by the open_basedir setting leads to PHP
warnings being raised.
Added error-suppression to the `is_executable($path)` call, too, per the bug noted just above.
The cited issue manifests as such without it:
```
ErrorException in ExecutableFinder.php line 63:
is_executable(): open_basedir restriction in effect. File(/usr/share/php) is not within the allowed path(s): (/usr/share/php:/tmp:/usr/share/phpmyadmin:/etc/phpmyadmin:/var/lib/phpmyadmin:/usr/local/zend/var/zray/extensions:/usr/local/zend/share:/usr/local/zend/var/plugins)
```
I've made the change as the executable goal is to find the executable. The fact that it does not find it is
part of the contract and it is not exceptional.
