client: update obsolete comments

1) there is nothing like main thread since
   3c7e8bfbb4 anymore, so remove
   it from documentation and update the doc accordingly.

2) use calling 'default queue' instead of 'main queue'. In the code
   we use display->default_queue, so it'll be easier the understand.

3) update some obsolete or unprecise pieces of documentation

v2. Not only remove out-of-date comment, but fix/remove more
    things across the wayland-client.[ch]

v3. fixes (rephrasing unclear paragraphs etc.)
    according to Pakka Paalanen notes (thanks)

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>

src/wayland-client.h

@@ -71,7 +71,7 @@ struct wl_proxy;
  * added to a queue. On the dispatch step, the handler for the incoming
  * event set by the client on the corresponding \ref wl_proxy is called.
  *
- * A wl_display has at least one event queue, called the <em>main
+ * A wl_display has at least one event queue, called the <em>default
  * queue</em>. Clients can create additional event queues with \ref
  * wl_display_create_queue() and assign \ref wl_proxy's to it. Events
  * occurring in a particular proxy are always queued in its assigned queue.
@@ -80,31 +80,27 @@ struct wl_proxy;
  * called by assigning that proxy to an event queue and making sure that
  * this queue is only dispatched when the assumption holds.
  *
- * The main queue is dispatched by calling \ref wl_display_dispatch().
- * This will dispatch any events queued on the main queue and attempt
- * to read from the display fd if its empty. Events read are then queued
- * on the appropriate queues according to the proxy assignment. Calling
- * that function makes the calling thread the <em>main thread</em>.
+ * The default queue is dispatched by calling \ref wl_display_dispatch().
+ * This will dispatch any events queued on the default queue and attempt
+ * to read from the display fd if it's empty. Events read are then queued
+ * on the appropriate queues according to the proxy assignment.
  *
  * A user created queue is dispatched with \ref wl_display_dispatch_queue().
- * If there are no events to dispatch this function will block. If this
- * is called by the main thread, this will attempt to read data from the
- * display fd and queue any events on the appropriate queues. If calling
- * from any other thread, the function will block until the main thread
- * queues an event on the queue being dispatched.
+ * This function behaves exactly the same as wl_display_dispatch()
+ * but it dispatches given queue instead of the default queue.
  *
  * A real world example of event queue usage is Mesa's implementation of
  * eglSwapBuffers() for the Wayland platform. This function might need
- * to block until a frame callback is received, but dispatching the main
+ * to block until a frame callback is received, but dispatching the default
  * queue could cause an event handler on the client to start drawing
  * again. This problem is solved using another event queue, so that only
  * the events handled by the EGL code are dispatched during the block.
  *
- * This creates a problem where the main thread dispatches a non-main
+ * This creates a problem where a thread dispatches a non-default
  * queue, reading all the data from the display fd. If the application
  * would call \em poll(2) after that it would block, even though there
- * might be events queued on the main queue. Those events should be
- * dispatched with \ref wl_display_dispatch_pending() before
+ * might be events queued on the default queue. Those events should be
+ * dispatched with \ref wl_display_dispatch_(queue_)pending() before
  * flushing and blocking.
  */
 struct wl_display;