Fix backlog request with size greater than remaining backlog.

Before, backlog would only be added to the buffer after receiving the full amount requested.  However, this would not work properly if the buffer didn't have the requested amount of backlog.  In that case, none of the requested backlog would ever be displayed.  This fixes the issue by adding all the received backlog to a single list at the CoreConnection level so that it is not necessary to keep a backlog stash in the buffer itself.