add debug print statement on SIGINT

messaging/messaging_pyx.pyx

@@ -84,6 +84,7 @@ cdef class SubSocket:
     if msg == NULL:
       # If a blocking read returns no message check errno if SIGINT was caught in the C++ code
       if errno.errno == errno.EINTR:
+        print("SIGINT received, exiting")
         sys.exit(1)
 
       return None