Fix: ein:tb-show did not work in shared-output buffer

It did not work because ein:get-notebook does not work.  Notebook
is not well defined in shared-output buffer since it knows only
about kernel (through cell).  This reflect the design that kernel
and notebook is well decoupled.

lisp/ein-kernel.el

@@ -58,6 +58,7 @@ FIXME: document other slots."
   after-execute-hook
   kernelinfo)
 
+(defalias 'ein:kernel-id 'ein:$kernel-kernel-id)
 
 (defstruct ein:$kernelinfo
   "Info related (but unimportant) to kernel

lisp/ein-traceback.el

@@ -79,10 +79,10 @@
   (unless
       (ein:and-let* ((tb-data (ein:get-traceback-data))
                      (url-or-port (ein:get-url-or-port))
-                     (notebook (ein:get-notebook))
-                     (nb-name (ein:notebook-name notebook))
+                     (kernel (ein:get-kernel))
+                     (kr-id (ein:kernel-id kernel))
                      (tb-name (format ein:tb-buffer-name-template
-                                      url-or-port nb-name)))
+                                      url-or-port kr-id)))
         (ein:tb-popup (ein:tb-new tb-name) tb-data)
         t)
     (error "No traceback is available.")))

lisp/ein.el

@@ -44,6 +44,7 @@
   "Ask server to create a new notebook and open it in a new buffer." t)
 
 (autoload 'ein:notebook-name "ein-notebook")
+(autoload 'ein:kernel-id "ein-kernel")
 
 (autoload 'ein:connect-to-notebook-command "ein-connect" nil t)
 (autoload 'ein:connect-to-notebook         "ein-connect" nil t)