Description:
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When JSON_NUMERIC_CHECK is used with json_encode, it looks at every string that is printed, including for property names, and checks whether to display it as an integer instead.  However, JSON mandates that all property names be represented as double-quoted strings, and displaying them as integers violates the spec.

The attached patch (against the php-5.3.8 tarball, should apply cleanly against SVN 5.3 branch) fixes this by masking out the JSON_NUMERIC_CHECK flag while outputting string properties.

Test script:
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$output = (object)array();
$output->{"1"} = "5";
echo json_encode($output, JSON_NUMERIC_CHECK);


Expected result:
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{"1":5}

Actual result:
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{1:5}