• Disable parallel build when clean install is enabled
  (gh#197, gh#198, shawnlaffan++)
  
• Dropping support for Perl 5.8.1, 5.8.2 and 5.8.3. For now AB will install
  on these versions of Perl, but a warning will be issued, along with a 3
  minute sleep at configure time. Please upgrade to 5.8.4 (or preferrably
  5.32). Starting July 1st, AB will refuse to install on these elderly Perls.
  (gh#200, gh#201)