Ping/highlight support

This had one big show-stopping bug: sometimes sublime text 2 sent a blanking patch when switching to a pinged buffer. It looks like `window.open_file()` creates an empty view for a bit, and we weren't checking whether the view was done loading before deciding to send a patch. Mega-oops. Fixed in 67742298c631342cedb7ddf90095320ea6efc55c