- Fix (again) partial piece avoidance for seeds
   - Fix several partial piece (temp file) leaks,
     some uncovered by previous rarest-first fixes, some in end game
   - Don't lose all DHT peers if we stop quickly (backport from update branch)
   - Explore a kbucket if it's less than 3/4 full (backport from update branch)

     and 'f9d82ac84936c56dc92691842757e8cc354511e2'

            (tickets #715 and #743)
 * SystemVersion: Centralize more methods here

Let's not direct people to see how to configure their browser at
http://www.i2p2.i2p/htproxyports when you need to have your proxy configured to go there!

   - Add peer test throttling
   - Peer test packet count fixes
   - Adjust peer test timeouts and add backoff
   - Reject relays and peer tests from same /16
   - More peer test cleanup and log tweaks
 * Transports:
   - Enforce minimum peer port
   - Warn on low router ports