`_setStream` supports “Unknown” resource type.

The `is_resource` function will return `false` for “Unknown” resource.
This patches does not throw an exception when one tries to set an
resource with such a type. Why? Because when applying some computations
after having disconnected a stream for example, the resource is
considered as “Unknown” but the associated node (its “environment”) is
still valid for computations.

Concrete example with `Hoa\Socket`: broadcasting a message after the
disconnection.
[auto] Merge from Stream

    • #ad839ca — `_setStream` supports “Unknown” resource type. (Ivan Enderlin, 2014-07-24)

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Merge branch 'master' of /var/lib/git/repositories/Library/Stream