libctf, next, hash: add dynhash and dynset _next iteration

libctf, next, hash: add dynhash and dynset _next iteration

This lets you iterate over dynhashes and dynsets using the _next API.
dynhashes can be iterated over in sorted order, which works by
populating an array of key/value pairs using ctf_dynhash_next itself,
then sorting it with qsort.

Convenience inline functions named ctf_dyn{hash,set}_cnext are also
provided that take (-> return) const keys and values.

libctf/
	* ctf-impl.h (ctf_next_hkv_t): New, kv-pairs passed to
	sorting functions.
	(ctf_next_t) <u.ctn_sorted_hkv>: New, sorted kv-pairs for
	ctf_dynhash_next_sorted.
	<cu.ctn_h>: New, pointer to the dynhash under iteration.
	<cu.ctn_s>: New, pointer to the dynset under iteration.
	(ctf_hash_sort_f): Sorting function passed to...
	(ctf_dynhash_next_sorted): ... this new function.
	(ctf_dynhash_next): New.
	(ctf_dynset_next): New.
	* ctf-inlines.h (ctf_dynhash_cnext_sorted): New.
	(ctf_dynhash_cnext): New.
	(ctf_dynset_cnext): New.
	* ctf-hash.c (ctf_dynhash_next_sorted): New.
	(ctf_dynhash_next): New.
	(ctf_dynset_next): New.
	* ctf-util.c (ctf_next_destroy): Free the u.ctn_sorted_hkv if
	needed.
	(ctf_next_copy): Alloc-and-copy the u.ctn_sorted_hkv if needed.