GUAC-746: Create new threads for new connections.
GUAC-746: Add surface dup/sync function.
GUAC-824: Synchronize new users with existing display.
GUAC-746: Add functions for sending/receiving file descriptors across processes.
GUAC-746: Migrate to client process storage.
GUAC-746: Create socketpair and fork for new processes.
GUAC-745: Log connection ID after NULL check.
GUAC-745: Close socket file descriptor automatically upon free. Add free handler to nested sockets while we're at it (fixes GUAC-354).