insert some more slack for indices in LU

Use doubly linked list for LU indices so that updating is less cumbersome.


git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1316 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

H/clause.h

@@ -52,6 +52,7 @@ typedef struct logic_upd_index {
     struct logic_upd_index *ParentIndex;
   } u;
   struct logic_upd_index *SiblingIndex;
+  struct logic_upd_index *PrevSiblingIndex;
   struct logic_upd_index *ChildIndex;
   /* The instructions, at least one of the form sl */
   yamop            ClCode[MIN_ARRAY];