(tags-table-parent-pointer-list): Doc fix; elts are now 3-elt lists.

(tags-table-parent-pointer-list): Doc fix; elts are now 3-elt lists.
(tags-next-table): Save tags-table-list in tags-table-parent-pointer-list
and then set it to tags-included-tables.
Restore tags-table-list from tags-table-parent-pointer-list.
(tags-find-table-in-list): Renamed from tags-table-list-member.
Search included tables.  Take new arg MOVE-TO; if t, frob list pointers.
(tags-table-including): Save tags-table-list in tags-table-parent-pointer-list.
Set tags-table-list to the passed TABLES value.
(visit-tags-table-buffer): When CONT is nil, pop all
tags-table-parent-pointer-list state before doing anything else.
Don't do list frobnication when CONT is 'same.
Call tags-find-table-in-list instead of tags-table-list-member; let it do
list frobnication when it succeeds.