* src/vteint.h: add.  Move private VteTerminal stuff which needs to be shared
	with other modules in the library here.
* src/vtedraw.c, src/vtedraw.h: add get_char_width(), for use in drawing the
	cursor.
* src/vte.c(vte_invalidate_cursor_once): if the character under the cursor
	doesn't fit into its cell, expose the column to the right of it so
	that we can paint into the adjacent cell.
* src/vte.c(vte_terminal_paint): when clearing the area behind the cursor or
	drawing the hollow rectangle to indicate its position when we don't
	have focus, use the visible width of the character instead of just
	assuming it will fit.  This complies better with assertion 2.