Fork cause 5 causing network splits

[Isabello]

When a node receives a block at the same height it does a simple check here: https://github.com/LiskHQ/lisk/blob/development/modules/blocks.js#L1341

This code basically says take the newest block we have and throw the old block away. This is incorrect. We need to approach this issue with the logic that the old blocks should be kept in every situation, as they will have the most adoption on the network and be forged by the correct delegate.

the revised code would look like this:

if (block.id < __private.lastBlock.id) {
   if (block.timestamp < __private.lastBlock.timestamp) {
   	library.logger.info('Last block loses');
   	return self.deleteLastBlock(cb);
   } else {
   	library.logger.info('Last block should not lose');
   	return setImmediate(cb);
   }
} else {
   library.logger.info('Newly received block wins');
   return setImmediate(cb);
}

[karmacoma]

The following is a revised strategy courtesy of @4miners and @Isabello.

• Compare blocks based on timestamp, not block id.
• Warn when delegate detected forging on multiple nodes.
• Delete both last block and its parent on fork 1.
• Immediately receive block on fork 5 resolution.

[Isabello]

Actually will reference in new issue.