Testing infrastructure: mocktime fixes

New, undocumented-on-purpose -mocktime=timestamp command-line
argument to startup with mocktime set. Needed because
time-related blockchain sanity checks are done on startup, before a
test has a chance to make a setmocktime RPC call.

And changed the setmocktime RPC call so calling it will not result in
currently connected peers being disconnected due to inactivity timeouts.

src/init.cpp

@@ -868,6 +868,9 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     fAlerts = GetBoolArg("-alerts", DEFAULT_ALERTS);
 
+    // Option to startup with mocktime set (used for regression testing):
+    SetMockTime(GetArg("-mocktime", 0)); // SetMockTime(0) is a no-op
+
     // ********************************************************* Step 4: application initialization: dir lock, daemonize, pidfile, debug log
 
     // Initialize elliptic curve code

src/rpcmisc.cpp

@@ -378,10 +378,19 @@ UniValue setmocktime(const UniValue& params, bool fHelp)
     if (!Params().MineBlocksOnDemand())
         throw runtime_error("setmocktime for regression testing (-regtest mode) only");
 
-    LOCK(cs_main);
+    // cs_vNodes is locked and node send/receive times are updated
+    // atomically with the time change to prevent peers from being
+    // disconnected because we think we haven't communicated with them
+    // in a long time.
+    LOCK2(cs_main, cs_vNodes);
 
     RPCTypeCheck(params, boost::assign::list_of(UniValue::VNUM));
     SetMockTime(params[0].get_int64());
 
+    uint64_t t = GetTime();
+    BOOST_FOREACH(CNode* pnode, vNodes) {
+        pnode->nLastSend = pnode->nLastRecv = t;
+    }
+
     return NullUniValue;
 }