cleanup tests for whether a python file is a user file or a library file

src/chatdbg/chatdbg_pdb.py

@@ -134,8 +134,12 @@ def _is_user_frame(self, frame):
     def _is_user_file(self, file_name):
         if file_name.endswith(".pyx"):
             return False
-        elif file_name == "<string>":
+        elif file_name == "<string>" or file_name.startswith('<frozen'):
+            # synthetic entry point or frozen modules
             return False
+        elif file_name.startswith('<ipython'):
+            # stdin from ipython session
+            return True
 
         for path in self._library_paths:
             if os.path.commonpath([file_name, path]) == path: