patch 8.0.1590: padding in list type wastes memory

Problem:    Padding in list type wastes memory.
Solution:   Reorder struct members to optimize padding. (Dominique Pelle,
            closes #2704)

src/structs.h

@@ -1260,21 +1260,22 @@ struct listwatch_S

/*
 * Structure to hold info about a list.
 * Order of members is optimized to reduce padding.
 */
struct listvar_S
{
    listitem_T	*lv_first;	/* first item, NULL if none */
    listitem_T	*lv_last;	/* last item, NULL if none */
    int		lv_refcount;	/* reference count */
    int		lv_len;		/* number of items */
    listwatch_T	*lv_watch;	/* first watcher, NULL if none */
    int		lv_idx;		/* cached index of an item */
    listitem_T	*lv_idx_item;	/* when not NULL item at index "lv_idx" */
    int		lv_copyID;	/* ID used by deepcopy() */
    list_T	*lv_copylist;	/* copied list used by deepcopy() */
    char	lv_lock;	/* zero, VAR_LOCKED, VAR_FIXED */
    list_T	*lv_used_next;	/* next list in used lists list */
    list_T	*lv_used_prev;	/* previous list in used lists list */
    int		lv_refcount;	/* reference count */
    int		lv_len;		/* number of items */
    int		lv_idx;		/* cached index of an item */
    int		lv_copyID;	/* ID used by deepcopy() */
    char	lv_lock;	/* zero, VAR_LOCKED, VAR_FIXED */
};

/*

src/version.c

@@ -766,6 +766,8 @@ static char *(features[]) =

static int included_patches[] =
{   /* Add new patch number below this line */
/**/
    1590,
/**/
    1589,
/**/