_multiprocessing Connection methods don't check if handle is valid or 
not. If you close the socket/pipe, Python may crash on operations, 
especially in poll() on FD_SET(...handle, &rdfs).

Example of crash:
----------------------
import _multiprocessing
obj = _multiprocessing.Connection(755)
obj.close()
obj.poll()
----------------------

Attached patch is a proposition of fix to check handle in all 
Connection methods using the handle.