DLIST changes

[Sam Liddicott]

In re-basing my work on alpha15 I'm bitten by some dlist changes.

I've worked round them, but suggest some changes to DLIST.
I suggest a change (1) and an additional choice of changes (2).

For my own code I shall adopt (1) and (2.2) for the time being.


1. addition of DLIST_ADD_END with 2 parameters.

It is fine that the third parameter is ignored, but we can at least 
avoid requiring it to be specified for new code.


2. support of void* list-heads.

I make use of void* private pointers, like 
smbcli_request.asyc.private_data as list heads.

As more dlist macros do things like both of these internally:
   a. (list)->prev
   b. (list)=(p)->next
the list argument to the macros can't include a typecast. This was true 
in some cases but now is true in more cases.

So I propose EITHER:

2.1 additional 3-parameter variants which actually use the third 
parameter - like this:

#define DLIST_ADD(list, p, type) \
do { \
     type *list_typed=&(list); \
     DLIST_ADD(*list_typed, p); \
     } \
while(0);

OR
2.2 a DLIST_TYPE to be invocable as a filthy outer-macro like this:

#define DLIST_TYPE(list, type, DLIST_STATEMENT) do { \
   type *THELIST=&(list); \
   DLIST_STATEMENT; \
} while(0)

and so void* list heads might be used with nested macros like this; the 
actual list and type being specified in the outer-macro and *THELIST 
being used as the first parameter in the inner macro:

DLIST_TYPE(creq->async.private_data, struct async_info_map *, 
DLIST_ADD_END(*THELIST, async));


I am happy to write the code if someone in authority will give an idea 
of what approach (if any) would be acceptable.

Sam