Merge the streamlining changes from #911. Fixes #911.

git-svn-id: file:///svn/tokudb@4500 c7de825b-a66e-492c-adef-691d508d4ae1

newbrt/brt-internal.h

@@ -189,8 +189,8 @@ unsigned int toku_brtnode_pivot_key_len (BRTNODE, struct kv_pair *); // Given th
 struct brt_cursor {
     struct list cursors_link;
     BRT brt;
-    DBT key;
-    DBT val;
+    DBT key, val;             // The key-value pair that the cursor currently points to
+    DBT prevkey, prevval;     // The key-value pair that the cursor pointed to previously.  (E.g., when we do a DB_NEXT)
     int is_temporary_cursor;  // If it is a temporary cursor then use the following skey and sval to return tokudb-managed values in dbts.  Otherwise use the brt's skey and skval.
     void *skey, *sval;
     OMTCURSOR omtcursor;

newbrt/brt.h

@@ -53,6 +53,12 @@ int toku_brt_cursor_delete(BRT_CURSOR cursor, int flags, TOKUTXN);
 int toku_brt_cursor_close (BRT_CURSOR curs);
 BOOL toku_brt_cursor_uninitialized(BRT_CURSOR c);
 
+DBT *brt_cursor_peek_prev_key(BRT_CURSOR cursor);
+DBT *brt_cursor_peek_prev_val(BRT_CURSOR cursor);
+DBT *brt_cursor_peek_current_key(BRT_CURSOR cursor);
+DBT *brt_cursor_peek_current_val(BRT_CURSOR cursor);
+void brt_cursor_restore_state_from_prev(BRT_CURSOR cursor);
+
 typedef struct brtenv *BRTENV;
 int brtenv_checkpoint (BRTENV env);