Fix for stuck blockchain download at blocks 21000, 21500 and 22000. Now getblocks() message is issued after connection to new node if waited longer than MAX_TIME_SINCE_BEST_BLOCK seconds.
part 2 of [Fix for stuck blockchain download at blocks 21000, 21500 and 22000]. Issuing getblocks() command also after seeing an error during ProcessBlock().
Merge pull request #14 from eagleflies/master

Fix for stuck blockchain at blocks 21000, 21500 and 22000.