BCrypt wrap bug detected

[mo7ty]

Starting from BCrypt release - v5.0.0:

• Passing hashpw a password longer than 72 bytes now raises a
  ValueError. Previously the password was silently truncated, following the
  behavior of the original OpenBSD bcrypt implementation.

The internal check for BCrypt wrap bug in _BcryptCommon/_finalize_backend_mixin()/detect_wrap_bug(indent)`, is failing with:

ValueError: password cannot be longer than 72 bytes, truncate manually if necessary (e.g. my_password[:72])

Reproducible running test_handlers_bcrypt with latest BCrypt release.

[chapmajs]

Submitted PR #21 as an improved fix which does not require pinning bcrypt down.

[mo7ty]

Closing issue as per #25 (comment).