fix: Bottle.__setattr__ breaks data descriptors

fixes: bottlepy#1450

bottle.py

@@ -1122,8 +1122,7 @@ def __exit__(self, exc_type, exc_value, traceback):
     def __setattr__(self, name, value):
         if name in self.__dict__:
             raise AttributeError("Attribute %s already defined. Plugin conflict?" % name)
-        self.__dict__[name] = value
-
+        object.__setattr__(self, name, value)
 
 ###############################################################################
 # HTTP and WSGI Tools ##########################################################

docs/faq.rst

@@ -107,7 +107,7 @@ Bottle catches all Exceptions raised in your app code to prevent your WSGI serve
 
     import bottle
     app = bottle.Bottle() 
-    app.catchall = False #Now most exceptions are re-raised within bottle.
+    app.catchall = False  # Now most exceptions are re-raised within bottle.
     myapp = DebuggingMiddleware(app) #Replace this with a middleware of your choice (see below)
     bottle.run(app=myapp)
 

test/test_exc.py

@@ -33,6 +33,9 @@ def test_noncatched_error(self):
         @bottle.route('/')
         def test(): raise SomeError
         bottle.request.environ['exc_info'] = None
-        bottle.catchall = False
+        self.app.catchall = False
+        with self.assertRaises(SomeError):
+            self.urlopen("/")
+        self.app.catchall = True
         self.assertStatus(500, '/')
         self.assertInBody('SomeError')