Adjustment to console signal-handling

Do not explicitly interrupt the kernel, because the subprocess
already gets the interrupt.  Once we properly prevent this, then
the interrupt can be restored.

Also, the KeyboardInterrupt is still raised if not executing, in order
to restore the prompt.

In ipkernel, the interrupt is ignored during poll, and restored after
the loop exits, to prevent it being swallowed in future code that
expects normal sigint behavior.

IPython/frontend/terminal/console/app.py

@@ -22,6 +22,8 b' from IPython.frontend.terminal.ipapp import TerminalIPythonApp, frontend_flags a'
 from IPython.utils.traitlets import (
     Dict, List, Unicode, Int, CaselessStrEnum, CBool, Any
 )
+from IPython.utils.warn import warn,error
+
 from IPython.zmq.ipkernel import IPKernelApp
 from IPython.zmq.session import Session, default_secure
 from IPython.zmq.zmqshell import ZMQInteractiveShell
@@ -114,12 +116,22 b' class ZMQTerminalIPythonApp(TerminalIPythonApp, IPythonMixinConsoleApp):'
                         ipython_dir=self.ipython_dir, kernel_manager=self.kernel_manager)
 
     def handle_sigint(self, *args):
-        self.shell.write('KeyboardInterrupt\n')
-        if self.kernel_manager.has_kernel:
-            self.kernel_manager.interrupt_kernel()
+        if self.shell._executing:
+            if self.kernel_manager.has_kernel:
+                # interrupt already gets passed to subprocess by signal handler.
+                # Only if we prevent that should we need to explicitly call
+                # interrupt_kernel, until which time, this would result in a 
+                # double-interrupt:
+                # self.kernel_manager.interrupt_kernel()
+                pass
+            else:
+                self.shell.write_err('\n')
+                error("Cannot interrupt kernels we didn't start.\n")
         else:
-            print 'Kernel process is either remote or unspecified.',
-            print 'Cannot interrupt.'
+            # raise the KeyboardInterrupt if we aren't waiting for execution,
+            # so that the interact loop advances, and prompt is redrawn, etc.
+            raise KeyboardInterrupt
+            
 
     def init_code(self):
         # no-op in the frontend, code gets run in the backend

IPython/zmq/ipkernel.py

@@ -198,6 +198,9 b' class Kernel(Configurable):'
             except KeyboardInterrupt:
                 # Ctrl-C shouldn't crash the kernel
                 io.raw_print("KeyboardInterrupt caught in kernel")
+        # stop ignoring sigint, now that we are out of our own loop,
+        # we don't want to prevent future code from handling it
+        signal(SIGINT, default_int_handler)
         if self.eventloop is not None:
             try:
                 self.eventloop(self)