- Return False when a ping has been sent, so current instance isn't trashed
  and replaced by ping's internal expectPacket.
- Make current idleEvent instance handle ping's timeout, to avoid creating
  a new event for each ping sent in relation to an existing event.
- Don't call expectPacket from ping when given a msg_id, meaning it is
  related to an existing event.
- Add a minimal delay of 5 seconds between 2 pings.
- Update event tests

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1713 71dcc9de-d417-0410-9af5-da40c76e7ee4