Start traces after extra sinks are started

Previously, if you configured a trace to use an
extra sink, you'd get a noproc error. Addresses
issue #296 on github.

src/lager_app.erl

@@ -208,7 +208,6 @@ start(_StartType, _StartArgs) ->
     start_handlers(?DEFAULT_SINK,
                    get_env(lager, handlers, ?DEFAULT_HANDLER_CONF)),
 
-    ok = add_configured_traces(),
 
     lager:update_loglevel_config(?DEFAULT_SINK),
 
@@ -223,6 +222,8 @@ start(_StartType, _StartArgs) ->
     %% Now handle extra sinks
     configure_extra_sinks(get_env(lager, extra_sinks, [])),
 
+    ok = add_configured_traces(),
+
     clean_up_config_checks(),
 
     {ok, Pid, SavedHandlers}.