[syslog-ng] [PATCH (3.4) 0/1]: value-pairs: Add value_pairs_foreach_sorted().

The patch that will follow shortly implements a value_pairs_foreach_sorted() function, that can be used for multiple purposes in the future: - Template functions that want to format their output with keys always in a predictable order. - Various other parts of the code, that work better when operating on a sorted collection. I'm submitting it separately, so that it'll be easier for me to build upon it in the not too distant future. (And because I almost forgot to send it, even though it was origianlly made in early november...)