Fix sync wedge corner case:
It could happen if a connection went into standby mode, while
it was the one which had requested the next span, and that span
was still waiting for the data, and that peer is not on the
main chain. Other peers can then start asking for that data
again and again, but never get it as only that forked peer does.
And various other fixes
If monerod is started with default sync mode, set it to SAFE after
synchronization completes. Set it back to FAST if synchronization
restarts (e.g. because another peer has a longer blockchain).
If monerod is started with an explicit sync mode, none of this
automation takes effect.
This was broken by the reorg fix, since we now have to add blocks
regardless of their starting height. We now check whether we know
the parent for the first block in the next span, or whether it was
requested. If neither, it's an orphan. If it is not known, but was
requested, we wait to get that block.
Add get_fork_version and add_ideal_fork_version to core so
cryptonote_protocol does not have to need the Blockchain
class directly, as it's not in its dependencies, and add
those to the fake core classes in tests too.
When a node is dropped, we stop considering its claimed blockchain
height as a factor in the target height calculation. This prevents
a runaway chain from being still thought to be the target even if
the nodes carrying it are dropped.
We won't even talk to a peer which claims a wrong version
for its top block. This will avoid syncing to known bad
peers in the first place.
Also add IP fails when failing to verify a block.
Connections can be dropped by the net_node layer,
unbeknownst to cryptonote_protocol, which would then
not flush any spans scheduled to that connection,
which would cause it to be only downloaded again
once it becomes the next span (possibly after a small
delay if it had been requested less than 5 seconds
ago).
A block queue is now placed between block download and
block processing. Blocks are now requested only from one
peer (unless starved).
Includes a new sync_info coommand.
All code which was using ip and port now uses a new IPv4 object,
subclass of a new network_address class. This will allow easy
addition of I2P addresses later (and also IPv6, etc).
Both old style and new style peer lists are now sent in the P2P
protocol, which is inefficient but allows peers using both
codebases to talk to each other. This will be removed in the
future. No other subclasses than IPv4 exist yet.
