adding post_mortem, similar to pdb

[CamDavidsonPilon]

@tamentis, I was having difficulty debugging a Spark job locally, and my friend pointed to your repo. My Spark job was throwing an exception inside some library on the worker node, so set_trace wasn't enough. I added this post_mortem function, and got great results! The work flow was:

import external_lib

def some_function_on_worker_node():
   import rpdb
   try:
     external_lib.failing_func()
  except:
      rpdb.post_mortem()

and nc 127.0.0.1 4444 got me right into the library's broken parts.

Thanks for this little library!

[tamentis]

Thanks for this update, very useful. I didn't even know about pdb.post_mortem().