Cleaned up all list iterations, added macro named LIST_FOREACH.

Previously you would have to do something like this:

for (type foo = (type) list_get_first(list); foo; foo = (type) list_get_next(list)
{
    /* code */
}

Now, you can instead write this as:

LIST_FOREACH(type, foo, list,
{
    /* code */
})

Basically, boilerplate stuff including the casting is gone.

src/util/list.h

@@ -57,5 +57,9 @@ extern void* list_get_prev(struct linked_list*);
 extern struct node* list_get_first_node(struct linked_list*);
 extern struct node* list_get_last_node(struct linked_list*);
 
+#define LIST_FOREACH(TYPE, ITEM, LIST, BLOCK) \
+		for (ITEM = (TYPE) list_get_first(LIST); ITEM; ITEM = (TYPE) list_get_next(LIST)) \
+			BLOCK
+
 #endif /* HAVE_UHUB_LINKED_LIST_H */