Wake and sleep events with "push back" data

This module's watch_read function, which is monkeypatched into
Danga::Socket, sets up an AnyEvent io event watcher on reads; but in
the case where synthetic reads ("push_back_read") are in effect, this
event will never fire.  This case can be detected, and the bit flipped
as in a previous change.  It also has a converse, which is to clear it
in the same situations.

lib/Danga/Socket/AnyEvent.pm

@@ -962,9 +962,15 @@ sub watch_read {
                 $self->event_read() unless $self->{closed};
             }),
         );
+        if ( $PushBackSet{$fd} ) {
+            $self->{event_watch} |= POLLIN;
+        }
     }
     else {
         $watchers->[0] = undef;
+        if ( $PushBackSet{$fd} ) {
+            $self->{event_watch} &= ~POLLIN;
+        }
     }
 }