Update to 0.51
    
    - New upstream release 0.51
      - Documentation updated courtesy of Mike Caron
      - Croak if attempt to freeze BerkeleyDB object (CPAN RT#69985)
      - Rework FETCHSIZE (CPAN RT#75691)
    - BR: perl(AutoLoader), perl(Carp), perl(Exporter) and perl(IO::File)
    - Anticipate RHEL 7 having libdb
    - Mention in %description that this module doesn't support db1
    - Don't need to remove empty directories from buildroot
    - Don't use macros for commands
    - Don't need to BR: bundled perl(Test::More)