Display error when duplicate block received
Fix logic for nSyncStarted (only increases when headers actually arrive).
Request headers while we don't have the headers (fix to headersfirst8)
Add nLastDataPos variable for partial message tracking.
Rearrange ProcessMessages
Add variables for tracking block download progress.
reword to show peer is not stalling, but key.
Add block stall logic to cater for scenarios where disconnect is beneficial.
Move "received block" message so that we can include the height in the debug message.
Keep track of average stall times - so that timeouts can be adjusted accordingly.
Log concurrent downloads
Debug when a block is incoming.
Improve getheader requests
Improve getheaders (recv) logging
Improve getblocks (reception) logging
Use syncheight instead of startheight for broadcasting block invs
Only respond to getblocks requests that are asking for substantially newer block invs.
Change check whether to send block inv after UpdateTip
Add nodeid to inactivity tracking
Add debug "tx" and "tx2" options