fix calling `UNLOCK()` in `xerror_redirect_unlocked()`
fix a bug in `backtrace` that didn't test correctly bash version

- `backtrace` needs bash version 4.0 or higher.  But the version test
  code was wrong.
fix a bug in `backtrace` that didn't test correctly bash version

- `backtrace` needs bash version 4.0 or higher.  But the version test
  code was wrong.
fix bytes -> string conversion error in python3