• Fix weakened reference cloning via deferred weakening (fixes #15)
  
• Fix memory leak when cloning non-existent hash values (fixes #42)
  
• Fix segfault when cloning DBI database handles (fixes #27)
  
• Rewrite t/09-circular.t to fix SEGV on CPAN Testers (fixes #54)
  
• Replace static recursion_depth with stack parameter
  
• Fix C++ style comments in Clone.xs for C89 portability