Update to 1.863
    
    - New upstream release 1.863
      - On Cygwin, silently use Mutex in MCE::Channel when Threads is specified for
        better performance
      - New defer capability in MCE::Signal, which applies to MCE::Shared 1.863;
        see POD section labled "DEFER SIGNAL" in MCE::Signal
      - Reverted $child->exit back to sending the SIGQUIT signal in MCE::Child now
        that MCE::Shared::Server 1.863 defers signal during IPC
      - Improved reliability for spawning MCE and MCE::Child inside threads
        including nested parallelization, made possible using a global lock
        $MCE::_GMUTEX
      - Updated signal handling in mce-examples/framebuffer on GitHub