Inconsistent errors

[norpan]

These two tests should give the same error:

    { "doc": {"bar": [1, 2]},
      "patch": [{"op": "add", "path": "/bar/8", "value": "5"}],
      "error": "Out of bounds (upper)" }

and

{ "comment": "add item to array at index > length should fail",
      "doc": ["foo", "sil"],
      "patch": [{"op":"add", "path": "/3", "value": "bar"}],
      "error": "index is greater than number of items in array" }