- add a config item vda_host_timeout.
A host that hasn't done a scheduler RPC for this long
is considered dead.
- a host that's not running a version 7+ client is considered dead
- host.cpu_efficiency (an otherwise unused field) is used
as a flag for dead hosts
- the scheduler clears the flag if the client is v7+
- vdad sets the flag for hosts where last RPC is old
- before choosing a host for chunk download,
vdad checks its client version.
svn path=/trunk/boinc/; revision=26059