- support VNC version 3.3 (macos "Screen Sharing" builtin client)
- wait until client has requested an update prior to sending framebuffer data
- don't send an update if no framebuffer updates detected
- increase framebuffer poll frequency to 30Hz, and double that when
kbd/mouse input detected
- zero uninitialized array elements in rfb_send_server_init_msg()
- fix overly large allocation in rfb_init()
- use atomics for flags shared between input and output threads
- use #defines for constants
This work was contributed by Marko Kiiskila, with reuse of some earlier
work by Henrik Gulbrandsen.