Collect sync request for during the sync interval time just
like before but instead of using XSync to send get-input-focus
requests and block for replies when the sync interval timer
fires, we're now just sending get-input-focus requests using
XCB and give each back-end server the sync-interval time to
respond before we block.
This provides significantly better performance, especially
with high latency connections.
The default sync batch interval of 100ms provides good
performance for back-ends servers with round-trip times
somewhat less than 100ms and is not long enough to make
the batch processing noticeably on low latency connections.
