wsi/x11: Uncork enqueueing multiple presents
The conditional being deleted here is "the image we just presented is
still not presented yet", we clear present_queued when we receive a
PresentCompleteNotify
indicating that the server now thinks the pixmap
is presented (but maybe not idle). The spec, however, says:
Queueing an image for presentation defines a set of queue
operations, including waiting on the semaphores and submitting a
presentation request to the presentation engine. However, the scope
of this set of queue operations does not include the actual
processing of the image by the presentation engine.
PresentCompleteNotify
is precisely "the presentation engine thinks this
has been done" so that ain't right.