merged branch martinml/master (PR #705)

Commits
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3eecc60 Silence chmod() warnings (operation not permitted) when using CIFS mounts and possibly other cases.

Discussion
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Silence chmod() warnings (operation not permitted) when using CIFS

When using chmod() in a CIFS mount (NTFS) in Linux, Twig 1.6.5 in PHP 5.3.3 throws a warning:

    Warning: chmod(): Operation not permitted in /smb/.../Twig/Environment.php on line 1052

There may be other combinations that trigger this warning. Related Symfony issue: https://github.com/symfony/symfony/issues/2125