Fix merging of EventTree lints

src/python/jat.py

         self.children = []
         self.rest = [e for e in events]
         self.head = head
+        self._lints = []
         while self.rest:
             if self.peek().startswith('SESSION.'):
                 self.pop()
                 return out
             else:
                 out.append(self.pop())
-        self.lints += [Lint('could not find: %s' % final_etype, out)]
+        self._lints += [Lint('could not find: %s' % final_etype, out)]
         return out
 
     @property
         lints = []
         for e in self.children:
             lints += e.lints
-        return lints
+        return self._lints + lints
 
 
 class Phase(EventTree):