Send repeated MSEARCHes for all types of device list refresh, stopping one iteration after we start receiving responses.  Poor quality wifi on iOS devices currently risks a Refresh() call leading to all devices being removed.  (This may still happen but they'd be quickly discovered again now, making Refresh() more accurately reflect the state of the network.)
Merge branch 'master' of ssh://core.linn.co.uk/home/git/ohnet