Make ignoring errors optional

[argv-minus-one]

Currently, graceful-fs does two things:

1. Recovering from errors:

• EMFILE, EAGAIN
• Some cases of EACCES and EPERM on Windows

2. Ignoring certain unrecoverable errors:

• EINVAL and EPERM from chown, lchown, and fchown
• lutimes, lchmod, and lchown silently fail if unavailable

The former should always be safe: the requested operation does happen, just not right away. The latter, however, may or may not be safe: some applications (installers, unarchivers) don't care about chown failures, but other applications (system scripts, backup tools) do care.

Please add some way to opt out of ignoring unrecoverable errors (perhaps by moving the error recovery part into a separate module that can be required by itself).