do not dump 404 traces

lib/sinatra/base.rb

@@ -787,9 +787,9 @@ module Sinatra
     # Error handling during requests.
     def handle_exception!(boom)
       @env['sinatra.error'] = boom
-      dump_errors!(boom) if settings.dump_errors?
+      status boom.respond_to?(:code) ? Integer(boom.code) : 500
+      dump_errors! boom if settings.dump_errors? and server_error?
       raise boom if settings.show_exceptions? and settings.show_exceptions != :after_handler
-      @response.status = boom.respond_to?(:code) ? Integer(boom.code) : 500
 
       if not_found?
         headers['X-Cascade'] = 'pass'

test/settings_test.rb

@@ -306,6 +306,29 @@ class SettingsTest < Test::Unit::TestCase
       get '/'
       assert body.include?("RuntimeError") && body.include?("settings_test.rb")
     end
+
+    it 'does not dump 404 errors' do
+      klass = Sinatra.new(Sinatra::Application)
+
+      mock_app(klass) {
+        enable :dump_errors
+        disable :raise_errors
+
+        error do
+          error = @env['rack.errors'].instance_variable_get(:@error)
+          error.rewind
+
+          error.read
+        end
+
+        get '/' do
+          raise Sinatra::NotFound
+        end
+      }
+
+      get '/'
+      assert !body.include?("NotFound") && !body.include?("settings_test.rb")
+    end
   end
 
   describe 'sessions' do