More descriptive short message

IPython/html/services/sessions/handlers.py

@@ -58,7 +58,7 b' class SessionRootHandler(IPythonHandler):'
             except NoSuchKernel:
                 msg = ("The '%s' kernel is not available. Please pick another "
                        "suitable kernel instead, or install that kernel." % kernel_name)
-                status_msg = 'Kernel not found'
+                status_msg = '%s not found' % kernel_name
                 self.log.warn('Kernel not found: %s' % kernel_name)
                 self.set_status(501)
                 self.finish(json.dumps(dict(message=msg, short_message=status_msg)))