* src/genwidths, src/uniwidths: add data for tracking ambiguous-width Unicode
	characters.
* src/iso2022.c, src/iso2022.h: add _vte_iso2022_is_ambiguous() for checking if
	a character is ambiguous, and _vte_iso2022_ambiguous_width() for
	guessing how wide it should be based on the current locale.  Rename
	_vte_iso2022_get/set_width to ...encoded_width to clarify the intent,
	ditto for the related macros.
* src/table.c,src/trie.c: use renamed macros for reading encoded widths.
* src/iso2022.c(_vte_iso2022_substitute_single,_vte_iso2022_substitute): handle
	ambiguous widths properly, and always encode a width.
* src/Makefile.am: use the default LDFLAGS, I think.
* src/vte.c,src/vte.h: add vte_terminal_set_background_tint_color().
* src/vte.c(vte_terminal_unrealize): unhook from background update sources,
	because we may not have a display after that.
* src/vte.c(vte_terminal_size_allocate): only queue a background update if
	we're in transparent ...