Turn wchar iterator into a class

Turn wchar iterator into a class

This changes wchar_iterator from charset.c into a real C++ class, then
updates the users to use the class.  This lets us remove some cleanups
in favor of the class' destructor.

2016-10-12  Tom Tromey  <tom@tromey.com>

	* valprint.c (generic_emit_char, count_next_character)
	(generic_printstr): Update.
	* charset.c (struct wchar_iterator): Move to charset.h.
	(wchar_iterator::wchar_iterator): Rename from
	make_wchar_iterator, turn into a constructor.
	(wchar_iterator::~wchar_iterator): Rename from
	do_cleanup_iterator, turn into a destructor.
	(make_cleanup_wchar_iterator): Remove.
	(wchar_iterator::iterate): Rename from wchar_iterate.  Remove
	"iter" argument.  Update.
	* charset.h: Include <vector>.
	(class wchar_iterator): New class, from old struct
	wchar_iterator.
	(make_wchar_iterator, make_cleanup_wchar_iterator): Don't
	declare.