recover from failures to accept a socket successfully. Problem suggested
by this:
> It would appear (from two "panic: closef: count < 0" failures in less
> than 12 hours) that Darren's fix to accept(2) for lost file descriptors
> isn't quite correct. His fix inserts a call to closef() to handle one
> of several possible error conditions. However everywhere else in the
> socket code in the same file where falloc() cleanup is necessary the
> function used is ffree().
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