Fix tuple argument order to remove backend

See PR #306 for details. This is a backport.

src/lager.erl

@@ -210,7 +210,16 @@ stop_trace(Backend, Filter, Level) ->
 stop_trace({Backend, Filter, Level}) ->
     stop_trace(Backend, Filter, Level).
 
-stop_trace_int({Backend, _Filter, _Level} = Trace) ->
+%% Important: validate_trace_filters orders the arguments of
+%% trace tuples differently than the way outside callers have
+%% the trace tuple.
+%%
+%% That is to say, outside they are represented as 
+%% `{Backend, Filter, Level}'
+%%
+%% and when they come back from validation, they're
+%% `{Filter, Level, Backend}'
+stop_trace_int({_Filter, _Level, Backend} = Trace) ->
     {Level, Traces} = lager_config:get(loglevel),
     NewTraces =  lists:delete(Trace, Traces),
     _ = lager_util:trace_filter([ element(1, T) || T <- NewTraces ]),