Update to 5.3104
    
    - New upstream release 5.3104
      - Clarify licensing terms
      - Don't install private Module::Install extension (CPAN RT#103482)
      - Move verbose testing to a private module, and implement it in a way that
        doesn't require editing the Makefile after it is generated
      - Require File::Slurp instead of including it, to avoid potential problems
        like this:
        http://www.cpantesters.org/cpan/report/86a0145a-e52b-11e4-a1d1-8536eb4f9f07
      - Miscellaneous fixes for Windows compatibility, including weaking the
        invalid mailbox test so that it only looks for output from grepmail, and
        not any "broken pipe" message from the OS