Replace setInventoryKnown with a rolling bloom filter.

Mruset setInventoryKnown was reduced to a remarkably small 1000
 entries as a side effect of sendbuffer size reductions in 2012.

This removes setInventoryKnown filtering from merkleBlock responses
 because false positives there are especially unattractive and
 also because I'm not sure if there aren't race conditions around
 the relay pool that would cause some transactions there to
 be suppressed. (Also, ProcessGetData was accessing
 setInventoryKnown without taking the required lock.)

src/net.cpp

@@ -2342,7 +2342,7 @@ unsigned int SendBufferSize() { return 1000*GetArg("-maxsendbuffer", DEFAULT_MAX
 CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNameIn, bool fInboundIn) :
     ssSend(SER_NETWORK, INIT_PROTO_VERSION),
     addrKnown(5000, 0.001),
-    setInventoryKnown(SendBufferSize() / 1000)
+    setInventoryKnown(50000, 0.000001)
 {
     nServices = 0;
     hSocket = hSocketIn;
@@ -2369,6 +2369,7 @@ CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNa
     nSendOffset = 0;
     hashContinue = uint256();
     nStartingHeight = -1;
+    setInventoryKnown.reset();
     fGetAddr = false;
     fRelayTxes = false;
     pfilter = new CBloomFilter();