respond to signals when readline is waiting for input (bug #54444) * input.cc (internal_input_event_hook_fcn): Also call octave_quit. Since we will always call octave_quit, don't remove self from command_editor event hook list if input_sys no longer has hook functions registered. (Fadd_input_event_hook, Fremove_input_event_hook): Don't remove internal_input_event_hook_fcn from command_editor event hook list if input_sys no longer has hook functions registered. (input_system::m_initialized): New data member. (input_system::initialize): Don't allow initialization more than once. Call command_editor::add_event_hook to install internal_input_event_hook_fcn.

--- a/libinterp/corefcn/input.h	Thu Sep 10 13:49:46 2020 +0900
+++ b/libinterp/corefcn/input.h	Wed Sep 09 23:57:20 2020 -0400
@@ -191,6 +191,8 @@
 
     hook_function_list m_input_event_hook_functions;
 
+    bool m_initialized;
+
     std::string gnu_readline (const std::string& s, bool& eof) const;
   };