Tag lager_msg messages with a {log, ...} tuple

Helps with pattern matching.

include/lager.hrl

@@ -58,11 +58,11 @@
     lager_util:level_to_num(Level) =< element(1, lager_mochiglobal:get(loglevel, {?LOG_NONE, []}))).
 
 -define(NOTIFY(Level, Pid, Format, Args),
-    gen_event:notify(lager_event,lager_msg:new(io_lib:format(Format, Args),
+    gen_event:notify(lager_event, {log, lager_msg:new(io_lib:format(Format, Args),
             lager_util:format_time(),
             Level,
             [{pid,Pid},{line,?LINE},{file,?FILE},{module,?MODULE}],
-            [])
+            [])}
         )). 
 
 %% FOR INTERNAL USE ONLY

src/lager.erl

@@ -74,8 +74,8 @@ dispatch_log(Severity, Metadata, Format, Args, Size) when is_atom(Severity)->
                         A when is_list(A) ->safe_format_chop(Format,Args,Size);
                         _ -> Format
                     end,
-                    gen_event:sync_notify(Pid, lager_msg:new(Msg, Timestamp,
-                            Severity, Metadata, Destinations));
+                    gen_event:sync_notify(Pid, {log, lager_msg:new(Msg, Timestamp,
+                                Severity, Metadata, Destinations)});
                 _ -> 
                     ok
             end

src/lager_console_backend.erl

@@ -67,7 +67,7 @@ handle_call(_Request, State) ->
     {ok, ok, State}.
 
 %% @private
-handle_event(Message,
+handle_event({log, Message},
     #state{level=L,formatter=Formatter,format_config=FormatConfig} = State) ->
     case lager_util:is_loggable(Message, L, ?MODULE) of
         true ->

src/lager_file_backend.erl

@@ -91,7 +91,7 @@ handle_call(_Request, State) ->
     {ok, ok, State}.
 
 %% @private
-handle_event(Message,
+handle_event({log, Message},
     #state{name=Name, level=L,formatter=Formatter,formatter_config=FormatConfig} = State) ->
     case lager_util:is_loggable(Message,L,{lager_file_backend, Name}) of
         true ->

test/lager_test_backend.erl

@@ -54,7 +54,7 @@ handle_call({set_loglevel, Level}, State) ->
 handle_call(_Request, State) ->
     {ok, ok, State}.
 
-handle_event(Msg, 
+handle_event({log, Msg},
         #state{level=LogLevel,buffer=Buffer,ignored=Ignored} = State) ->
         case lager_util:is_loggable(Msg, LogLevel, ?MODULE) of
             true ->   {ok, State#state{buffer=Buffer ++