MoarVM/MoarVM — pull request #73 by hoelzro (2014-01-30 21:35:39+00:00)
Title: Clear fd when closing a file handle to prevent "dangling" descriptors

We can run into a situation with MoarVM where a double close can
close an arbitrary, innocent file. Consider:

```perl6
my $fh := nqp::open($filename); # let's say it's FD 3
# do stuff
nqp::close($fh);
my $other_fh := nqp::open($other_filename); # 3 again!
nqp::close($fh); # closes 3! o_O
```