Allow the user to define a "no_such_file_handle" function which is analogous to
"command_not_found_handle" but also runs when a command contains a "/".

--- execute_cmd.c	2020-10-12 07:16:13.000000000 -0700
+++ execute_cmd.c	2021-08-03 09:39:01.138503014 -0700
@@ -5438,6 +5438,11 @@
 #  define NOTFOUND_HOOK "command_not_found_handle"
 #endif
 
+/* Name of a shell function to call when a command path does not exist. */
+#ifndef NOSUCHFILE_HOOK
+#  define NOSUCHFILE_HOOK "no_such_file_handle"
+#endif
+
 static int
 execute_disk_command (words, redirects, command_line, pipe_in, pipe_out,
 		      async, fds_to_close, cmdflags)
@@ -5587,7 +5592,23 @@
 	  wl = make_word_list (make_word (NOTFOUND_HOOK), words);
 	  exit (execute_shell_function (hookf, wl));
 	}
+      else if (strchr (pathname, '/') && access (pathname, F_OK))
+	{
+	  hookf = find_function (NOSUCHFILE_HOOK);
+	  if (hookf == 0)
+	    goto run_shell_execve;
+
+	  without_job_control ();
+
+#if defined (JOB_CONTROL)
+	  set_sigchld_handler ();
+#endif
+
+	  wl = make_word_list (make_word (NOTFOUND_HOOK), words);
+	  exit (execute_shell_function (hookf, wl));
+	}
 
+run_shell_execve:
       /* Execve expects the command name to be in args[0].  So we
 	 leave it there, in the same format that the user used to
 	 type it in. */