Imply the |safe on tojson in templates and change escaping logic

flask/app.py

@@ -659,7 +659,7 @@ class Flask(_PackageBoundObject):
             session=session,
             g=g
         )
-        rv.filters['tojson'] = json.htmlsafe_dumps
+        rv.filters['tojson'] = json.tojson_filter
         return rv
 
     def create_global_jinja_loader(self):
@@ -1707,13 +1707,6 @@ class Flask(_PackageBoundObject):
             rv = func(exc)
         request_tearing_down.send(self, exc=exc)
 
-        # If this interpreter supports clearing the exception information
-        # we do that now.  This will only go into effect on Python 2.x,
-        # on 3.x it disappears automatically at the end of the exception
-        # stack.
-        if hasattr(sys, 'exc_clear'):
-            sys.exc_clear()
-
     def do_teardown_appcontext(self, exc=None):
         """Called when an application context is popped.  This works pretty
         much the same as :meth:`do_teardown_request` but for the application