I/O error in JSON read

[andychu]

After #672

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I looked into it more, and while I didn't find the exact issue, the py-yajl binding we're using for JSON isn't great. It needs to use a more straightforward loop like the example here.

https://lloyd.github.io/yajl/

$ bin/osh -c 'json read :x < configure'
lexical error: invalid char in json text.
                                       #!/bin/sh # # POSIX shell scrip
                     (right here) ------^
  json read :x < configure
       ^~~~
[ -c flag ]:1: json read: parse error
Error closing descriptor 0: [Errno 9] Bad file descriptor
osh I/O error: Bad file descriptor

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Though it doesn't look like the binding closes the file descriptor, which would be the obvious bug