More BidiFdWatcher fixes.
More BidiFdWatcher fixes.

In BaseFdWatcher, event_flags need to be cleared after an event is
processed (for a BidiFdWatcher, only one event flag is cleared).
When re-enabling an FdWatcher, don't enable channels that have
pending events - this indicates a Bidi watcher with event already
queued.

davmac314/dasynq,davmac314/dasynq