[patch] dlinklist.h rewrite

[tridge at samba.org]

Hi Jeremy,

I've pushed a testsuite for the dlinklist.h macros to my dlist-rewrite
branch. It also includes a const fix for DLIST_CONCATENATE().

At some stage we could get rid of the 'type' arguments to
DLIST_ADD_END(), DLIST_DEMOTE() and DLIST_CONCATENATE() as they are
not used any more. I thought I'd leave in those for now as it keeps
the changes to a minimum and we could remove the type arguments once
we are sure the changes have not introduced any problems.

Cheers, Tridge