fix bug in initial-block-headers download

saves several gigabytes of bandwidth
thanks to Cryptoslave of Anoncoin for this fix.

src/main.cpp

@@ -4477,7 +4477,10 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
             if (inv.type == MSG_BLOCK) {
                 UpdateBlockAvailability(pfrom->GetId(), inv.hash);
-                if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
+                if (!fAlreadyHave && !fImporting && !fReindex && IsInitialBlockDownload() && !mapBlocksInFlight.count(inv.hash)) {
+                    // !IsInitialBlockDownload() is needed otherwise it start to download the same headers 
+                    // several time per peer and from all peers, wasting a lot of computing time and bandwidth
+                    
                     // First request the headers preceding the announced block. In the normal fully-synced
                     // case where a new block is announced that succeeds the current tip (no reorganization),
                     // there are no such headers.

src/main.h

@@ -73,7 +73,7 @@ static const int MAX_SCRIPTCHECK_THREADS = 16;
 /** -par default (number of script-checking threads, 0 = auto) */
 static const int DEFAULT_SCRIPTCHECK_THREADS = 0;
 /** Number of blocks that can be requested at any given time from a single peer. */
-static const int MAX_BLOCKS_IN_TRANSIT_PER_PEER = 16;
+static const int MAX_BLOCKS_IN_TRANSIT_PER_PEER = 32;
 /** Timeout in seconds during which a peer must stall block download progress before being disconnected. */
 static const unsigned int BLOCK_STALLING_TIMEOUT = 2;
 /** Number of headers sent in one getheaders result. We rely on the assumption that if a peer sends