Update to 1.841
    
    - New upstream release 1.841
      - Disabled t/04_channel_threads testing on Unix platforms for Perl less than
        5.10.1; basically, the MCE::Channel::Threads implementation is not supported
        on older Perls unless the OS vendor applied upstream patches (i.e. works on
        RedHat/CentOS 5.x running Perl 5.8.x)
      - Added LIMITATIONS section to MCE::Channel::Threads