Implement the `broadcastIf` method.

This method broadcasts a message to a subset of nodes that respect a
given predicate. For example:

    $source->broadcastIf(
        function ( \Hoa\Socket\Node $node ) {

            return $node->getNumber() > 5;
        },
        'You are high!'
    );
[auto] Merge from Socket

    • #48bccfc — Implement the `broadcastIf` method. (Ivan Enderlin, 2014-08-06)

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