Use ?TOMBSTONE macro everywhere

src/lsm_btree_merger2.erl

@@ -6,6 +6,13 @@
 
 -export([merge/5]).
 
+-include("lsm_btree.hrl").
+
+%%
+%% Most likely, there will be plenty of I/O being generated by
+%% concurrent merges, so we default to running the entire merge
+%% in one process.
+%%
 -define(LOCAL_WRITER, true).
 
 merge(A,B,C, Size, IsLastLevel) ->
@@ -73,7 +80,7 @@ scan(BT1, BT2, Out, IsLastLevel, [{Key1,Value1}|AT]=AKVs, [{Key2,Value2}|BT]=BKV
             end,
             scan(BT1, BT2, Out2, IsLastLevel, AKVs, BT, Count+1);
 
-       (delete =:= Value2) and (true =:= IsLastLevel) ->
+       (?TOMBSTONE =:= Value2) and (true =:= IsLastLevel) ->
             scan(BT1, BT2, Out, IsLastLevel, AT, BT, Count);
 
        true ->
@@ -94,7 +101,7 @@ scan_only(BT, Out, IsLastLevel, [], Count) ->
             {ok, Count, Out}
     end;
 
-scan_only(BT, Out, true, [{_,delete}|Rest], Count) ->
+scan_only(BT, Out, true, [{_,?TOMBSTONE}|Rest], Count) ->
     scan_only(BT, Out, true, Rest, Count);
 
 scan_only(BT, Out, IsLastLevel, [{Key,Value}|Rest], Count) ->