wait -n' notifies on a job it returns; in posix mode, wait' defers notification on a reaped pid unless the shell is interactive, as posix now specifies

lib/readline/histfile.c

@@ -647,6 +647,7 @@ history_truncate_file (const char *fname, int lines)
 truncate_write:
   tempname = history_tempfile (filename);
 
+  rv = 0;
   if ((file = open (tempname, O_WRONLY|O_CREAT|O_TRUNC|O_BINARY, 0600)) != -1)
     {
       if (write (file, bp, chars_read - (bp - buffer)) < 0)