Spec clean-up
    
    - Explicitly require perl(Class::Accessor::Fast) unless we have rpm ≥ 4.9,
      which can auto-detect the dependency
    - Drop buildreq perl(Module::Install) - Makefile.PL explicitly uses the one
      bundled in inc/
    - Don't need to remove empty directories from buildroot
    - Use DESTDIR rather than PERL_INSTALL_ROOT
    - Make %files list more explicit
    - Don't use macros for commands
    - Drop %defattr, redundant since rpm 4.4
    - Improve %description and %summary