Install signal handler on each code run to protect against user code that

may modify it as well.  If we don't do this, on the next Ctrl-C python
itself will likely just crash completely.

IPython/Shell.py

@@ -4,7 +4,7 b''
 All the matplotlib support code was co-developed with John Hunter,
 matplotlib's author.
 
-$Id: Shell.py 2221 2007-04-06 02:58:37Z fperez $"""
+$Id: Shell.py 2222 2007-04-06 17:11:27Z fperez $"""
 
 #*****************************************************************************
 #       Copyright (C) 2001-2006 Fernando Perez <[e-mail]>
@@ -340,9 +340,6 b' class MTInteractiveShell(InteractiveShell):'
         # enough, because uses like macros cause reentrancy.
         self.code_queue = Queue.Queue()
 
-        # Track once we properly install our special sigint handler
-        self._sigint_handler_not_ready = True
-        
         # Stuff to do at closing time
         self._kill = False
         on_kill = kw.get('on_kill')
@@ -413,12 +410,8 b' class MTInteractiveShell(InteractiveShell):'
                 tokill()
             print >>Term.cout, 'Done.'
 
-        # Install sigint handler.  It feels stupid to test this on every single
-        # pass.  At least we keep track of having done it before...  We use a
-        # negative variable so we don't have to call 'not' every time
-        if self._sigint_handler_not_ready:
-            # Try only once...
-            self._sigint_handler_not_ready = False
+        # Install sigint handler.  We do it every time to ensure that if user
+        # code modifies it, we restore our own handling.
             try:
                 signal(SIGINT,sigint_handler)
             except SystemError: